The argon was collected in two operations. First the quantity made by absorption by magnesium in glass tubes with the water-pump circulator was purified. Later, after a second supply had been prepared by absorption in iron tubes, the mixture of argon and nitrogen was united with the first quantity and circulated, by means of the mercury circulator, in the gas-holder B. Attention will be drawn to the particular sample of gas employed in describing further experiments made with the argon.

By means of magnesium, about seven litres of nitrogen can be absorbed in an hour; the changing of the tubes of magnesium, however, takes some time; consequently the largest amount absorbed in one day was nearly thirty litres.

The principal objection to the oxygen method of isolating argon, as hitherto described, is the extreme slowness of the operation. An absorption of 30 c. c. of mixed gas means the removal of but 12 c. c. of nitrogen. At this rate eight hours are required for the isolation of 1 c. c. of argon, supposed to be present in the proportion of 1 per cent.

In extending the scale of operations we had the great advantage of the advice of Mr. Crookes, who a short time ago called attention to the flame rising from platinum terminals which convey a high-tension alternating electric discharge, and pointed out its dependence upon combustion of the nitrogen and oxygen of the air.1 Mr. Crookes was kind enough to arrange a demonstration at his own house with a small alternating current plant, in which it appeared that the absorption of mixed gas was at the rate of 500 c. c. per hour, or nearly twenty times as fast as with the battery. The arrangement is similar to that first described by Spottiswoode." The primary of a Ruhmkorff coil is connected directly with the alternator, no break or condenser being required, so that in fact the coil acts simply as a high-potential transformer. When the arc is established the platinum terminals may be separated beyond the initial striking distance.

The plant with which the large scale operations have been made consists of a De Meritens alternator, kindly lent by Professor J. J. Thomson, and a gas-engine. As transformer, one of Swinburne's hedgehog pattern has been employed with success, but the ratio of transformation (24:1) is scarcely sufficient. A higher potential, although perhaps not more efficient, is more convenient. The striking distance is greater, and the arc is not so liable to go out. Accordingly most of the work to be described has been performed with transformers of the Ruhmkorff type.

The apparatus has been varied greatly, and it cannot be regarded as having even yet assumed a completely satisfactory and final form. But it will give a suffi

2

Chemical News, vol. LXV, p. 301, 1892.

A mode of exciting an induction-coil. Philadelphia Magazine, vol. VIII, p. 390, 1829.

cient idea of the method if we describe an experiment in which a tolerably good account was kept of the air and oxygen employed. The working vessel was a glass flask of about 1500 c. c. capacity, and stood neck downwards over a large jar of alkali. As in the small scale experiments the leading-in wires were insulated by glass tubes, suitably bent and carried through the liquid up the neck. For the greater part of the length iron pipes were employed, but the internal extremities were of platinum, doubled upon itself at the terminals from which the discharge escaped. The glass projecting tubes must be carried up for some distance above the internal level of the liquid, but it is desirable that the arc itself should not be much raised above that level. A general idea of the disposition of the electrodes will be obtained from the figure (5). To ensure gas tightness these bends were occupied by mercury. A tube for the supply or withdrawal of gas was carried in the same way through the neck.

FIG. 5.

The Ruhmkorff employed in this operation was one of medium size. When the mixture was rightly proportioned and the arc of full length, the rate of absorp tion was about 700 c. c. per hour. A good deal of time was lost in starting, for especially when there is soda on the platinum, the arc is liable to go out if lengthened prematurely. After seven days the total quantity of air led in amounted to 7925 c. c. and of oxygen (prepared from chlorate of potash) 9137 c. c. On the eighth and ninth days oxygen alone was added, of which about 500 c. c. was consumed, while there remained about 700 c. c. in the flask. Hence the proportion in which the air and oxygen combined was as 79:96. On the eighth day there was about three hours' work, and the absorption slackened off to about one-quarter of the previous rate. On the ninth day (September 8th) the rate fell off still more,

and, after three hours' work, became very slow. The progress towards removal of nitrogen was examined from time to time with the spectroscope, the points being approximated and connected with a small Leyden jar. At this stage the yellow nitrogen line was faint, but plainly visible. After about four hours' more work the yellow line had disappeared, and for two hours there had been no visible contraction. It will be seen that the removal of the last part of the nitrogen was very slow, mainly on account of the large excess of oxygen present.

The final treatment of the residual 700 c. c. of gas was on the model of the small scale operations already described.

By means of a pipette the gas was gradually transferred to a large test tube standing over alkali. Under the influence of sparks (from battery and coil) passing all the while, the superfluous oxygen was consumed with hydrogen fed in slowly from a voltameter. If the nitrogen had been completely removed, and if there were no unknown ingredient in the atmosphere, the volume under this treatment should have diminished without limit. But the contraction stopped at a volume of 65 c. c., and the volume was taken backwards and forwards through this as a minimum by alternate treatment with oxygen and hydrogen added in small quantities, with prolonged intervals of sparking. Whether the oxygen or the hydrogen were in excess could be determined at any moment by a glance at the spectrum. At the minimum volume the gas was certainly not hydrogen or oxygen. Was it nitrogen? On this point the testimony of the spectroscope was equally decisive. No trace of the yellow nitrogen line could be seen even with a wide slit and under the most favorable conditions.

When the gas stood for some days over water the nitrogen line again asserted itself, and many hours' sparking with a little oxygen were required again to get rid of it. As it was important to know what proportions of nitrogen could be made visible in this way, a little air was added to gas that had been sparked for some time subsequently to the disappearance of nitrogen in its spectrum. It was found that about 13 per cent was clearly, and about 3 per cent was conspicuously, visible. About the same numbers apply to the visibility of nitrogen in oxygen when sparked under these conditions, that is, at atmospheric pressure, and with a jar in connection with the secondary terminals.

When we attempt to increase the rate of absorption by the use of a more powerful electric are further experimental difficulties present themselves. In the arrangement already described, giving an absorption of 700 c. c. per hour, the upper part of the flask becomes very hot. With a more powerful are the heat rises to such a point that the flask is filled with steam and the operation comes to a standstill. The remedy is to be found in the use of a larger vessel submerged, at any rate as

regards its upper portion, in water.

In the later experiments a globe of about 7 litres capacity, intended for showing the combustion of phosphorus in oxygen, was employed. The neck was inclined upwards at an angle of about 45° and was closed air-tight by a cork, through which were led the necessary tubes. The lower part of the globe is occupied by about 3 litres of a 5 per cent solution of caustic soda, the solution rising to within about half an inch of the platinum terminals. The upper half of the globe is kept cold by water applied externally. With this apparatus an absorption of 3 litres of mixed gas per hour can be attained,-about 3000 times the rate at which Cavendish could work.

9. DENSITY OF ARGON PREPARED BY MEANS OF OXYGEN.

isolated by

No direct determination has yet been made of the density of argon the oxygen method, but a fair estimate may be founded upon the data relating to the volumes already recorded, on the assumption that the accurately known densities of atmospheric and chemical nitrogen differ on account of the presence of argon in the former and that during the treatment with oxygen nothing is oxydized except nitrogen. Thus if

the law of mixtures gives :

D= density of chemical nitrogen,

D' =

atmospheric nitrogen,

D and L are both small, but they are known with fair

d

2

= 3.378. Thus if N, be 14 or O2 be 16, the density of argon is 20.6. It had been hoped that further data might have been obtained respecting the proportional volume of argon in atmospheric nitrogen, but accidents difficult to avoid in operations so risky and so extended have hitherto stood in the

10. DENSITY OF ARGON PREPARED BY MEANS OF MAGNESIUM.

way.

It has already been stated that the density of the residual gas from the first and preliminary attempt to separate oxygen and nitrogen from air by means of

magnesium was 19.086, and allowing for contraction on sparking with oxygen the density is calculable as 20.01. The following determinations of density were also made:

(a) After absorption in glass tubes, the water circulator having been used, and subsequent circulation by means of mercury circulator until the rate of contraction had grown slow:

162.843 cubic centimetres, measured at 757.7 mm. (corr.) pressure and 16°.81 C., weighed 0.2683 gramme. Hence,

Weight of litre at o° and 760 mm....

1.7541 grammes.

Density compared with hydrogen (O 16)............ 19.64

=

This gas was again circulated over red-hot magnesium for two days. Before circulation it contained nitrogen, as was evident from its spectrum; after circulating, nitrogen appeared to be absent, and absorption had completely stopped, and the density was again determined.

(b) 162.843 cubic centimetres, measured at 745.4 mm. (corr.) pressure and 17.25 C., weighed 0.2735 gramme. Hence,

Weight of 1 litre at 0° and 760 mm.

1.8206 grammes.

Density compared with hydrogen (0 = 16)............ 20.38

Several portions of this gas having been withdrawn for various purposes were somewhat contaminated with air, owing to leakage, passage through the pump, etc. All these portions were united in the gas-holder with the main stock, and circulated for eight hours, during the last three of which no contraction occurred. The gas removed from the system of tubes by the mercury-pump was not restored to the gas-holder, but kept separate.

(c) 162.843 cubic centimetres, measured at 758.1 mm. (corr.) pressure and 17o.09 C., weighed 0.27705 gramme. Hence,

Weight of litre at o° and 760 mm..

Density compared with hydrogen (0 = 16)...

1.8124 grammes. 20.28

The contents of the gas-holder were subsequently increased by a mixture of nitrogen and argon from 37 litres of atmospheric nitrogen, and after circulating, . density was determined. The absorption was, however, not complete.

(d) 162.843 cubic centimetres, measured at 767.6 mm. (corr.) pressure and 16°.31 C., weighed 0.2703 gramme. Hence,

Weight of litre at o° and 760 mm..

1.743 grammes.

Density compared with hydrogen (0 = 16)....

19.54