is not a sufficient reply to say that "there is a course of blowpipe instruction in almost every English chemical class or college." Every chemist who has been to Freiberg, or even to the American colleges, knows how inefficiently the blowpipe is taught, or rather, how effectually it is neglected in our otherwise excellent schools of chemistry. If this point be controverted, it will not be difficult to take one of our most generally received analytical textbooks, and show what extraordinary and incorrect statements are there made with regard to blowpipe analysis, nor does an inspection of some of the English pyrological instruments and apparatus at all reassure us. I have lately, incredible as it will seem, been shown an instrument as the only kind of blowpipe in use in a public laboratory in London, having an aperture at the jet, at least a quarter of an inch in diameter; and, to make matters worse, filled both with the blast and with aërated coal gas! I saw a youth blowing through such a machine as this by means of a mouthpiece cleverly extemporised with a glass funnel, and warned him that he would thus probably injure his lungs, a misfortune which would of course be attributed to the blowpipe," instead of to the personal use of such a tuyere as this.

(8). It may be as well to mention here that blowpipes like that devised by Von Frick, having the operator's breath, or blast from any other source, and the gas for ignition conveyed by the same tube, are utterly useless for these purposes; that Bunsen burners are useless for these purposes; that Fletcher's most ingenious, and no doubt otherwise invaluable "hot blast blowpipe" is almost useless for these purposes, which are most erroneously supposed to be always best effected by the greatest heat. Let any student who really wishes to learn this science produce a blue pyrocone from a candle by a hand blower, and then with a mouth blowpipe held in the other hand, direct a blast across this blue pyrocone, so as to dissect it; he finds it to be a solid mass of blue flame. If he now perform the same operation on the pyrocone from a gas jet, the pyrocone is found to be slightly hollow, while the pyrocone from a Bunsen burner has only the merest thin shell of circumscribing ignited gaseous matter. It is obvious, therefore, that the effect of holding the fragment or paste of a mineral or other essay, in the middle of these three pyrocones, must be different in each case; yet how seldom in England do we see a candle or oil lamp used for important results which can be obtained solely by its use?

(9). It is obvious that in order to properly systematise the science of blowpipe analysis, we ought to reduce it to as close analogy as may be with the procedure in ordinary chemical analysis, which has been found to answer so well. I have, therefore, in my method discarded the preliminary use of the salts borax and microcosmic sal', and commenced attacking substances with the pyracids "Boric and phosphoric anhydride." Boric acid, indeed, contrary to the account found in most of our chemical works, dissolves before the blowpipe no oxide whatever completely, except those of the alkaline metals, and that of silver a little, but its reactions thus are a thousand times more valuable than if it really (as we are told) dissolved all those, while, by adding pyrologically a very small proportion of alkali (not quite 5 per cent) we obtain a still acid menstruum which is itself extremely soluble in water. Phosphoric acid, on the other hand, is, before the blowpipe, the most powerful unmixed solvent in the world, dissolving gold leaf to a bluish violet glass quite rapidly. In either case we can further, if we like, obtain an acidulated water solution, in which precipitates can be produced by alkalies, &c., just as in "the wet way," but this process requires to be worked out, and shall not therefore be further alluded to here.

(10). It is necessary, however, to lightly touch upon one part of the subject, not invidiously but conscientiously, before proceeding to details. However invaluable the application of the symbolical and algebraical process o ratiocination may be, assuming its groundwork of facts to

*

be correct, to what may be termed the metaphysical chemistry of modern times, it seems insufficient when absolutely and completely substituted for practical knowledge, and reasoning in mere English, and, indeed, it is obvious that, in England at least, there is a tendency among our best writers, even on chemical metaphysics, to express their thoughts, not only in English, but in the very plainest English which has ever been in the possession of Her Majesty or her predecessors. There is no art so difficult of attainment as simplicity, and we may safely regard the value of an invention (or the description of one) in the inverse ratio to its complication. Whoever takes the trouble to compare the amazing hieroglyphical work of the communistical chemist Nacquet, translated into English the other day, with the luminous " essays of the marvellous apothecary Scheele ;† or Axiom V., Book I. of Newton's Optics, on the ratio between the sines of incidence and refraction in a ray of light, with the ordinary scientific account of the same simple law given in our modern mathematical or physical works, will soon see that the advantage in every essential particular remains with the adopters of expression by means of language. Besides, no one, not even the most eminent philosopher, can afford to discard the very great advantage of addressing himself to thousands-perhaps millions-of his fellow creatures, instead of to a few transcendentalists who cannot spread his opinions beyond their own clique.

REPORT

ON THE

DEVELOPMENT OF THE CHEMICAL ARTS
DURING THE LAST TEN YEARS.

By Dr. A. W. HOFMANN.
(Continued from vol. xxxii., p. 286.)

THENARD, on bringing peroxide of hydrogen into contact with his tongue, in order to ascertain its taste, found that it was whitened. The cuticle was also blackened, and at the same time a violent itching was excited. Litmus paper without any previous reddening was at once decolourised, as was also turmeric paper.

In 1863 Chevreul undertook comparative experiments on the bleaching power of hydrogen peroxide. Its concentrated solution speedily turned syrup of violets green, oxygen being set at liberty. For the following experiments dilute colour-solutions were used-namely, syrup of violets, tincture of litmus, extract of peach-wood, and extract of logwood. The results were as follows:

24 hrs...

80 hrs...

Litmus. Peach-wood. Logwood Slight Change to bleaching. rose.

Complete bleaching.

Turns

yellow

Almost complete bleaching.

Complete bleaching of all the solutions. Decolorisation is therefore effected less rapidly by peroxide of hydrogen than by chlorine. Tessié du Motay and Maréchals mention it as one of the agents which they propose for bleaching tissues, which, after treatment with permanganate of potash, they recommend to be steeped in a solution of peroxide of hydrogen. But it had been much earlier applied as a bleaching-agent by Thénard himself for a particular purpose-namely, for restoring old

The controversy at present proceeding between Dr. Frankland and Mr. Wanklyn in the CHEMICAL NEWS, with reference to water analysis, may be cited as an illustration of this point.

+ Schedle seems to have been a German, not a Swede, settled as a common apothecary, at Köping, in Sweden.

"Berichte über die Entwickelung der Chemischen Industr Während des Letzten Jahrzehends."

Chevreul, Comptes Rendus, lv., 735.

§ Bull. Soc. d'Encouragement, 1867, 472. Dingler, Polyt. Journal cxxc(?)iv., 526.

Pélouze and Frémy, Traité de Chimie, 1861.

oil-paintings and drawings. White-lead in old paintings, which has become blackened by the gradual action of sulphuretted hydrogen, is converted into sulphate of lead by dilute solutions of peroxide of hydrogen, and thus restored to its primitive colour. A fine drawing by Raffaelle, with superimposed white which had become spotted with black, was completely cleansed by a solution which contained at most five or six times its volume of available oxygen, and the paper did not suffer.

A peculiar, hitherto secret, application of this bleachingagent has been recently made public by A. v. Schrötter.* During the last few years bottles labelled " Eau de Fontaine de Jouvence, golden," and containing about 140 c.c. of a colourless liquid, have been sold by perfumers in great cities. The price demanded is about 20 francs, and to them, as it appears, is due that offensive blonde shade of hair which holds an intermediate place between ash-grey and bright yellow, and attracts the attention of the spectators and the curiosity of observers by its piquante unnaturalness. According to Schrötter this secret nostrum is merely a solution of hydrogen peroxide made stable by copious dilution, and by addition of a small quantity of acid, apparently nitric acid. According to Schrötter's careful examination it contained 6 volumes of available oxygen: 1000 grms. of the liquid would therefore contain 86 of available oxygen, or 18.3 of peroxide of hydrogen. As may be imagined, however, in case of an easily decomposable body, the bottles do not all contain solutions of equal strength. An examination conducted in the laboratory of the University of Berlin showed, in 1 volume of the solution, 94 to 98 vols. of available oxygen, corresponding to 13.6 grms. O, or 28.9 grms. H2O2, per litre. A bottle costing 20 francs yields the purchaser 2.5 to 4 grms. of this substance in solution, and effects its purpose completely, though slowly, within four to six days, thus strikingly illustrating the great efficacy of peroxide of hydrogen. The name of the perfumer who understands how to speculate so successfully upon the purses of his fair contemporaries, and who deserves to be known to posterity, is E. H. Thiellay, of London.

many individual cases it may be far from being true. It would therefore seem to be desirable to get rid of this uncertainty by constructing an instrument in which we are sure that the causes of variability are not allowed to operate.

These causes of variability I have attempted to get rid of in the following manner. With the help of Mr. Jordan, mechanician at Owens College, the following instrument has been constructed. It consists of a large mercurial thermometer with its bulb in the middle of a cubical castiron chamber, this chamber being of such massive material that its temperature will remain sensibly constant for some time. The chamber with its thermometer has a motion in azimuth round a vertical axis, A, and also a motion in altitude round a horizontal axis, B. A three inch lens, C, of 12 inches focal length is attached by means of a rod to the cubical chamber so as to move with it. The nature of this attachment will be seen in the figure. Thus the whole instrument may be easily moved into such a position that the lens as well as the upper side of the chamber which is parallel to the plane of the lens may face the sun, and an image of the sun be thrown through a hole, D, in the side of the chamber upon the thermometer bulb, E.

ON AN INSTRUMENT FOR MEASURING THE DIRECT HEAT OF THE SUN.+

By Prof. BALFOUR STEWART, LL.D., F.R.S.

THE instrument generally employed for giving the radiant energy of the sun's rays acts upon the following principle. In the first place the instrument is sheltered from the sun but exposed to the clear sky, say for five minutes; let the heat so lost be termed r. Secondly, the instrument is turned to the sun for five minutes; let the heat so gained be termed R. Thirdly, the instrument being row hotter than it was in the first operation, is turned once more so as to be exposed to the clear sky for five minutes while it is shielded from the sun; let the heat so lost be termed r'. It thus appears that r denotes the heat lost by convection and radiation united when the instrument, before being heated by the sun, is exposed for five minutes to the clear sky, while r' denotes the heat lost by these same two operations by a similar exposure after the instrument has been heated by the sun; and it is assumed that the heat lost from these two causes during the time when the instrument is being heated by the sun will be a mean between r and r', and hence that the whole effect of the sun's rays will be in reality

Now although this assumption may in the average of a great number of experiments represent the truth, yet in *Berl. Chem. Ces., 1874, 980.

chamber as in the figure. A screw, S, somewhat larger in The stem of the thermometer protrudes from the diameter than the bulb of the thermometer is made use of to attach the thermometer to its enclosure, and a smaller the thermometer to be properly adjusted and kept tight screw, S', pressing home upon india-rubber washers enables when in adjustment.

chamber is 2 inches, while the bulb of the thermometer is In the present instrument the internal diameter of the about 1 inches in diameter.

The scale of the thermometer is very open, more than the image of the sun given by the lens to heat the thermoan inch going to one degree. I have generally allowed meter bulb for one minute, during which time an increase has been produced. of temperature, not exceeding in any case two degrees,

As far as principle is concerned there appears to be no objection to the present instrument, nevertheless it is open to a very serious practical objection. The scale being so very open, the stem comprehends only a few degrees; frequently, therefore, the temperature is such that the extremity of the mercurial column is either below or above the stem. Now the thermometer has a small

tion well known to those who work with thermometers, it

i

s possible to add to or take away from the main body of mercury in the bulb so as to keep the end of the mercurial column always in the stem. But experience has convinced me that for a thermometer with such a large bulb, frequent manipulation of this kind is not unattended with danger to the bulb. On this account the instrument in its present form is, I conceive, unsuited for steady work in an observatory from year to year.

It is, however, possible without any appreciable sacrifice of the scientific principle of the instrument, to alter it in such a manner as to remedy this defect. Without altering the size of the bulb, I should propose for a permanent instrument a stem, say 18 inches long, with a bore of such diameter that the stem should embrace a range of temperature between 20° F. and 92° F. Thus somewhat less than 5 will go to the inch. The stem might be protected from the risk of accident by an appropriate shield. Let such a thermometer be heated for two minutes and the size of the lens be somewhat increased. In this case a rise of something like 5° F. will be obtained, and this heating effect might very easily be estimated to one-hundredth of the whole, while the same thermometer would serve for all the temperatures likely to occur in these islands during the course of the year.

I ought to add that a pasteboard cover gilded on the outside is made to surround the chamber, and also that between the lens and the chamber there is a pasteboard shield with a hole in it to permit the full rays from the lens to pass the object of this shield being to prevent rays from the sun or sky from reaching the instrument. In such an instrument r or the change taking place in the thermometer before exposure to the sun will in all probability completely disappear, while r' will be extremely small. At any rate we may be quite certain

that

will accurately represent the heating effect of the sun. We may probably suppose that in the same instrument the lens (which must always be kept clean) will always stop the same or nearly the same proportion of the solar rays. But the lens of one instrument may not stop the same proportion as that of another instrument. This, however, is no objection if it be borne in mind that the instrument is a differential one. In practice there would be some standard instrument which would be retained at a central observatory, and all other instruments would, before being issued, be compared with it. It would be thus possible to compare together the indications of various instruments working in different places provided that these, before being issued, had their co-efficients determined at the central observatory.

LABORATORY NOTES.

By SERGIUS KERN, St. Petersburg.

(1). On a Reagent for Uranium.-With potassium ferrocyanide (K4FeCy6) a solution of a uranic salt yields a brown precipitate of uranium ferrocyanide. The precipitate obtained much resembles the precipitate of copper ferrocyanide, but may be distinguished by the solubility of the precipitates in hydrochloric acid, viz., the uranium ferrocyanide dissolves easily even in diluted hydrochloric acid: the corresponding copper salt is insoluble in acids. This reaction may be used for the separation of copper from uranium. The uranium ferrocyanide dissolved in hydrochloric acid with a few drops of nitric acid gives a green colouration after being boiled for some minutes: this reaction is proposed as a test for uranium salts.

(2). On the Use of Cuprous Oxide.-This compound is easily prepared by boiling a solution of copper sulphate with sugar and an excess of caustic potash. As the Cuprous oxide (Cu2O) obtained in the form of a red powder

is soluble in ammonia and absorbs readily free oxygen, it is proposed to substitute it for the expensive pyrogallic acid now used in laboratories for the absorption of oxygen. Pyrogallic acid must be very carefully preserved, an account of the great avidity of this substance for oxygen, whilst cuprous oxide may be easily conserved in a dry state and when necessary dissolved in ammonia. A solution of cuprous oxide in ammonia absorbing oxygen gas turns blue, owing to the formation of cupric oxide (CuO). The solution of cupric oxide obtained may be again converted into a colourless solution of cuprous oxide (Cu2O) by placing in the liquor a clean copper wire. The formula CuO+Cu Cu2O explains this reaction.

ANALYSIS OF "TELL-TALE SUGAR LIQUOR "

FROM THE

SAFES OF TWO VACUUM SUGAR PANS.
By G. C. STEWART, F.C.S.,
Chemist at the Cappielow Sugar Refinery, near Greenock.

ALL vacuum sugar pans (exceptional instances overlooked) are furnished with "tell-tale sugar liquor" safes for catching any "sugar liquor," &c., which might accidentally or peradventure "otherwise boil over during the evaporating process in sugar refining.

These safes yield, when emptied, solutions which may vary in chemical composition according to a great variety tion of the pans may have a great deal to do with this, as has also the position in which the safe itself is fixed. If the pan is low set and very short in the swan's neck, ten to one but that the " liquor drawn from the safe of such a pan will be found upon analysis to be much richer in " sugar" and other organic matter than the "liquor" drawn from another pan high set and very lofty in the swan's neck.

of circumstances. First of all, the mechanical construc

Such is the case, and occasionally in sugar-boiling, when too much "salt" water is given to the condenser during the evaporating process, it not unfrequently happens that this excess of salt water finds exit by "more roads

than down the Torricellian tube."

When such an accident occurs, the "liquor" drawn from the safe will be found upon analysis to be almost salt water," and will actually taste salt.

64

NOTICES OF BOOKS.

Third Annual Report of the Board of Health of the City of Boston. 1875. Boston: Rockwell and Churchill. THIS issue contains no small amount of important and interesting matter. There is a paper on the ventilation of schools by Dr. F. W. Draper, which takes up a subject hitherto neglected by sanitary reformers. Prof. W. R. Nichols took samples of air in III school-rooms and submitted them to analysis. The proportion of carbonic acid ranged from 3 volumes in 1000 to 057, with a general average of 118. The greatest amount compatible with a healthy condition of the atmosphere is fixed by Professor Pettenkofer at o'7; the carbonic acid being regarded not so much as a dangerous body per se, but as the measure of contamination in an occupied room as arising from organic products thrown off from the lungs and skin. It need scarcely be said that an apartment where the carbonic acid rises to 3 parts in 1000 is a most unfit place for children to spend some five or six hours daily. The means employed, often the only means provided, to remedy this state of things is merely an additional evil. The windows are thrown open, and, as Dr. Draper puts it, "the inevitable wave of cold outside air sweeps over the uncovered heads of the children and a fresh accession of cases of bronchitis, or of more serious pulmonary affections, is the result." In the inspection of the "Chapman school, a room showed at the desk-level a temperature of 77°; three quarters-of-an-hour later the same room was revisited, when the thermometer indicated 617, a fall of 153. Between the two visits the teacher had aired' the room to some purpose; the air was pure enough, and the coughing and sneezing of the children gave warning that it was cold enough also. If such a sudden change should occur in the outside atmosphere it would be considered a fruitful cause of increased sickness in the community." We greatly fear that were similar investigations undertaken in England the results would be found not more satisfactory than those given in the report before us. It is at least certain that too many school-houses, instead of broad windows admitting those floods of light for which children instinctively crave, are provided with narrow, mediæval loop-holes, calculated to admit only a dim mysterious light, symbolical of anything but intelligence, and eminently calculated to make the pupils uneasy and fretful.

From the sanitary condition of schools we pass to a paper on the sewage question by Dr. W. L. Richardson, who appears to have swallowed the ex parte statements of certain English irrigationists without the time-honoured grain of salt recommended on such occasions. Thus he tells us that the existence of sewage farms, so far from being detrimental to the health of the vicinity, has actually a beneficial effect. As proof of this statement-and incidentally we must add, as a confirmation of the remark that statistics can prove anything-he quotes from Dr. Corfield the case of Norwood, where, thanks to the establishment of a sewage farm, the mortality has fallen from 18 to 12'07 per 10co. Post hoc, ergo propter hoc? "This improved death-rate is of course to be attributed to the increased vegetation produced by sewage irrigation." If luxuriant vegetation necessarily implies a low death-rate, what do we say to the Terai, the west coast of Africa, the tierras calientes of Mexico, to rice-fields and mangrove swamps? Admitting, for argument's sake, the Norwood case, we cannot overlook the facts detailed in the official report on Progress of India, for 1871 and 1872, by C. R. Markham, C.B. Here it appears that the epidemic of 1847 was more severe and more general in the irrigated districts than elsewhere. A medical committee of inspection recommended that irrigation should not be brought within 200 yards of the villages, and that the atter should be screened by a double row of trees, planted around the irrigated lands. If such are the effects of irrigation with clean water, applied, moreover, only when

needed by the crops, what must be the results of irrigation with sewage, carried on day by day? It must be clearly understood that if we pour any volatile liquid even upon the most perfect filter, evaporation takes place from the surface. If we keep the surface constantly moist, the evaporation is continuous, and if the liquid hold in solution any sewage gases these, too, must as by physical necessity be delivered into the atmosphere. Between a sewage farm and a polluted river there is simply this difference, that the former exposes a far broader evaporating surface. The vicinity of a sewage farm may here and there, for a few years, appear healthy. But just the same may be said of certain places where the utmost sanitary neglect prevails. We could point out villages where the only supply of water is either from shallow wells, separated from cesspools by only a few yards of chalk and gravel, or from roadside duck-ponds, receiving the drainage of cultivated lands and the oozings of farmyard dung heaps. Yet the death-rate is low, and the inhabitants healthy. Are we not from time to time informed of the health and vigour of nightmen, scavengers, knackers, bone-boilers, and others who are constantly engaged among putrescent matter? Are their no hale old gentlemen who have all their lives quaffed the waters of some City pump, sparkling with carbonic acid due to decomposing animal substances, and whom no physician nor chemist can convince of its unhealthiness? Such cases as that of Norwood either prove nothing or a great deal too much. If a sewage farm is healthy, sanitary reform is a needless luxury.

As to the "astounding results"-which are slow in taking the form of hard cash,-the "enormous crops," and the "most luxuriant vegetation," the eyes of the public are gradually being opened. At first we were told that sewage irrigation would render the application of manure superfluous; then it appeared that the dung of the stock kept upon the farm must be added; and now we find that the green crops are to be ploughed in to enrich the soil! Dr. Richardson exaggerates when he says that precipitation processes allow all the soluble matters in the sewage to escape with the effluent. He for gets, too, that of the combined nitrogen present in the sewage, a large part, varying from a quarter to two-thirds, goes off in the drainage from the irrigation farms. So that precipitation and irrigation alike fail to secure all the valuable matter contained in sewage. That in India and other hot, dry countries irrigation is often the one thing wanted to convert a desert into a garden, we fully admit. But in England, in average seasons, it is quite as clearly the one thing which is not wanted.

The report further contains the yearly results of the chemical examination of articles of diet, medicines, &c., as executed by the able chemist to the Board, Dr. W. R. Nichols. Special notice is given of a class of quack medicines largely sold under the name of bitters, but containing large proportions of alcohol, in one case as much as 59 per cent.

CORRESPONDENCE.

SAMPLING OF MILK FOR ANALYSIS.

To the Editor of the Chemical News. SIR,-Since the Sale of Food and Drugs Act came into operation, I have observed on several occasions that the mode of taking and dividing the samples of milk supplied to the analyst has an important influence on the comparative results of analyses made for the determination or the fat. I am sometimes called upon to analyse not only the sample left with me by the inspector, but also that left with the dealer, who is naturally anxious to know the result quickly instead of remaining in suspense, it may be, for weeks; and I have not unfrequently found,

under such circumstances, that the two analyses have differed in regard to fat to the extent of five or ten hundredths of a per cent. This difference I have traced to the method adopted by the inspectors in dividing the samples. The milk, when purchased, is put into a jug, and from this three bottles are filled. Many minutes often elapse between the making of the purchase and the subsequent dividing and sealing of the samples, during which time a partial separation of cream takes place, to an extent depending on the condition of the milk at the time, and, as a consequence, the bottle first filled will contain a milk somewhat richer in butter than the others. This difference would not have occurred in the divided samples obtained as they used to be under the old Act, for each sample was then taken in a bottle to the analyst, and by him divided after having been thoroughly mixed by shaking, which can be done in a bottle but not in a jug.

I have also found a want of accordance in the results of milk analyses arising from another and very different cause. I have been anxious to satisfy myself as to the usual amount of reduction in the proportion of fat which takes place in large vessels from which milk is being dipped out for sale both by retail and wholesale; and having had several experiments made in which milk has been dipped in successive quantities out of the tin churns containing about 16 gallons, and also out of the counterpans or tureens containing about 10 gallons each, I have found that when such quantities of milk have, by successive dippings, been divided into two parts, one consisting of what has been dipped out, and the other of what remained, on taking a sample from each as a milkman would take it, and estimating the fat, the mean of the two extremes has not coiucided with the proportion of fat contained in the original milk. In fact, it is impossible, in dealing with large quantities of milk, as the milkmen do, and using the same vessels, to get concordant results of that description. I have always found the mean of the extremes to be below the quantity present in the original sample, if in taking the sample the measure or dipper be plunged in vertically to the depth of an inch or two below the surface, for in that case the richer stratum of milk and cream on the surface is broken and dispersed and the measure filled from the poorer portion beneath.

A milkman can easily supply a sample of milk from a counter-pan, that shall be either richer or poorer in fat than a fair average sample of the whole would be by varying the mode of taking it, but it would be impossible, in the usual mode of serving milk, to ensure that the sample shall represent the mean of the whole.

My object in communicating this note is to show that samples of milk taken in the usual way from the large vessels in which it is kept and conveyed for sale, hardly can, and generally does not, fairly represent an average of the bulk from which they are taken in regard to the proportion of fat present.—I am, &c.,

17, Bloomsbury-square, December 28, 1875.

T. REDWOOD.

ESTIMATION OF MINUTE TRACES OF COPPER.

To the Editor of the Chemical News.

SIR, Will you allow me to draw attention to the fact that a process for the estimation of minute traces of copper, after precipitation of iron with ammonia, exactly similar to that given by Mr. Carnelley in your issue of this week (vol. xxxii., p. 308), was proposed by me in the CHEMICAL NEWS, vol. xxxii., p. 3, in an article on the analysis of minium, of which an abstract appears in the Journal of the Chemical Society for December last. It is fair to own that the principle was suggested by Mr. Carnelley's process for the estimation of iron, and I frankly confess that, with the splendid opportunities of experiment and investigation offered by the laboratory of Owens College, he has treated the subject with a thoroughness and precision which were unattainable by me, owing

partly to want of leisure, and partly to the fact that the method was improvised under pressure of the sudden necessity for giving a complete analysis of a series of remarkably pure samples of red lead. He will find, however, on referring to my paper, that I have drawn attention to the disturbing influence of ammoniacal salts, which I have proposed to neutralise by the preparation of a comparison liquid from one-half of the solution to be examined.

It would appear that the usefulness of colorimetry, and also of judgment by turbidity, which may be provisionally termed "nephelometry," might be widely extended by the elaboration of a thoroughly reliable process for determining the exact equivalence of columns of liquid of different lengths by the correspondence of their colour or appearance as viewed from the ends; such devices as the preparation of comparison liquids, or the intentional addition of foreign salts, might then be entirely dispensed with as follows:

Let two equal columns of the solution to be tested be taken, and let their exact measure be known; then let a different proportion of a standard solution of the ingredient to be determined be added to each-it will probably be convenient to add twice as much to one as to the other-and let the columns be made equivalent by shortening one of them. It will be evident that if the original solution was quite free from the substance sought, the comparative lengths of the columns will correspond with the proportions of standard solution added to each, or in the case supposed will be represented by the fraction 12 =; but, if the original solution did contain the substance to be determined, the value of the fraction will be altered, and the quantity present in the longer column, the bulk of which is known, may be determined by a simple equation.

2 10

where n, of course, represents the known quantity o ingredient added to the longer column by means of the standard solution.

The application of this principle may be rendered clearer by an example.

The difficulty of obtaining distilled water absolutely free from ammonia for use in Wanklyn's process of water analysis is well known, and it would be obviously very convenient to determine once for all the proportion of ammonia in a given sample; we might proceed thus: two columns measuring four ounces each are taken; to one of them is added standard ammonia solution equal to 0.0005 grain, to the other equal to o'oor grain ammonia, the column of stronger tint is shortened, after Nesslerising, until the colour, viewed from above or below, by means of an appropriate apparatus, exactly corresponds; if the distilled water was pure one column will be exactly onehalf the length of the other, if ammonia was present the fraction will be greater. Suppose it is, then9 (x + 0.001) = x+0'0005 14 which will give x=0'0004 grain.

The "appropriate apparatus" mentioned above is, so far as I am aware, still a thing of the future.-I am, &c., THOS. P. BLUNT, M.A. Oxon., F.C.S.

Shrewsbury, January 1, 1876.

COPPER IN BREAD,

To the Editor of the Chemical News. SIR,-Dr. Edmunds in his contribution to the CHEMICAL NEWS of December 31 (vol. xxxii., p. 311), throws doubt