the potash to unite with the oxide of lead, or a basic soluble salt had been formed, in which potash was present. Upon examining the nitrate of potash employed as a reagent in the first experiment, and which had been purchased for this purpose because it was labelled pure, it was found to contain alkaline chlorides, a circumstance to which the lead in the first experiment might in part be ascribed. A repetition of it with pure nitrate of potash and the hydrate and carbonate of lead, prepared by exposing lead to distilled water in an open vessel, gave but a faint discoloration with hydrosulphuric acid. I am inclined to ascribe to the reduction of the nitric acid much the greater part in the action of nitrates upon lead. "Action of Air. The importance of air in order to the action of a water upon lead has been intimated in the results already recorded. The following experiments confirm the observations of Yorke, Bonsdorff, and others, and, more recently, of Dr. Hayes, as expressed in his Report to the Consulting Physicians.* "Experiment 1.- June 17th. An apparatus consisting of a halfgill flask, containing lead scrapings and Cochituate water, filled to half its depth, the lead all below the surface of the water, was connected by a tube, bent twice at right angles, with a vessel of mercury. The cork uniting the tube and the flask was carefully covered with sealingwax. If, now, in the oxidation of the lead, oxygen should be withdrawn from the space above the water, mercury would rise to occupy its place. The mercury had risen, June 19th, three fourths of an inch; July 1st, four inches; July 22d, six inches; and in August the mercury passed over into the flask. Another similar apparatus prepared on the 16th of May showed, on the 10th of August, mercury at a height of 64 inches. "Experiment 2. A flask of a half-gill capacity was filled to two thirds its depth with distilled water, and boiled five minutes. While hot, and without delay, bars of bright lead were added, and the flask filled from another flask containing distilled water that had been boiling an equal length of time. In this condition a nicely-fitting cork was adjusted to the neck, and expeditiously sealed, so as to prevent the admission of air. Another flask was filled in the same manner with Cochituate water, and sealed. Both are in possession still. The bar in distilled water is quite as bright as when immersed, except around the end in contact with the glass, which has become a little coated. - The * Report of Consulting Physicians, Boston, 1848, p. 23. bar in Cochituate water was bright for some months, but has at length become slightly dimmed in small patches, which may be attributed to the less complete expulsion of the air by boiling, or the less accurate stopping of the flask, though at the time the experiment was made both were regarded as unobjectionable. "The following experiment shows how much is due to a change of water. The bars in the Cochituate remained quite bright, and those in the other waters were but slightly coated. Two bars in 15cc. for thirteen consecutive days, without changing the water, gave, in Cochituate, 0.500gr.; Croton, 0.500gr.; Fairmount, 0.500gr.; Jamaica, 1.000gr. "These experiments seemed to show that, without a renewal of the air, the action nearly or quite ceases after a short time. Professor Silliman, Jr., made a similar observation in his experiments with the various waters submitted to him for analysis by the Water-Commissioners in 1845. He used a large volume of water, and yet the bar remained quite bright. There was no alternate exposure to water and air. Christison remarks, that, while certain waters might doubtless be kept with safety in leaden cisterns, the covers of the cisterns should not be of lead, but of wood, since the moisture condensing on them, furnishing, as he observes, pure water, would act on the lead, and the product falling would poison the water. The joint action of air and water is here presented under exceedingly favorable circumstances. The corrosion of cisterns along the line where air and water meet might be expected. "It will be readily seen, from considering the important part .air plays, how rain-water must act with great vigor upon lead. It contains air, and is surrounded by air, and, aside from temperature, could not be more favorably constituted for acting upon lead. The well-known prevalence of lead maladies in Amsterdam, while leaden roofs were in use, and the restoration of health on their replacement with tile, find here a ready explanation. Dr. Dana has recorded an experiment with rain-water, which furnishes a valuable confirmation of what is stated above.* In a series of experiments with lead pipe of considerable length, if an interval of half a minute, or even less, occurred between the emptying of the pipe and refilling, there was invariably found lead in the water. This has been observed on a large scale in the practical service of lead pipe. Where from any cause the pipes have been empty for a length of time and then filled, the first water drawn con tains a very considerable quantity of lead. In the experiments of the preceding tables, the tubes intended to receive the bars were previously filled, and thus the transfer of the bar from one tube to another occupied scarcely a second of time. Even this short period was doubtless adequate to provide for some of the oxidation which the bar experienced.* Important as the office of air is, it is not adequate of itself to oxidate lead. A bar of lead scraped bright and placed in a desiccator over sulphuric acid remained undimmed for weeks, - during the whole time of the experiment. "Influence of Light and Organized Substances in Water. It is a familiar fact, that well-water recently drawn and exposed to the light and warmth a short time loses much of its air, and becomes insipid. Count Rumford has made this fact the foundation of an important investigation. His conclusions in relation to the joint effect of sunlight and solid miscible, but insoluble, substances in expelling the air from waters, and thus showing a difference between lake, river, pond, and reservoir waters, which are exposed to sunlight, and well or spring waters, which are concealed from it, are of great importance in this connection. I have made numerous experiments upon this subject, which, although still incomplete, taken in connection with the results of Count Rumford, go to establish the following positions : "1st. Well waters contain more air in solution than lake, river, and pond waters, as a class. 2d. Sunlight and heat falling upon water containing solid insoluble substances, organic tissues, or pulverulent matter, expel a portion of the gases. 3d. The germs of animalculæ being * I see, in the time between the emptying and filling of leaden pipes employed in experimenting, the explanation of much of the discrepancy between the results of different experimenters. If to this be added the unequal exposures to warmth and light which have been permitted by those engaged in experimenting, I am persuaded that most of the differences in results will be fully accounted for. He exposed spring water, containing, in a series of experiments, weighed quantities of raw silk, poplar cotton, sheep's wool, eider-down, hare's fur, cotton-wool, ravellings of linen, and Confervæ (hair-weed), to the sun's rays, and observed the quantity of air disengaged by each substance. It amounted in some cases to one eighth of the volume of water. Philosophical Papers, by Benjamin, Count Rumford, London, 1802, Vol. I., PP. 218-263. The observations of Wöhler in 1843 (Ann. der Chem, und Pharm., Bd. XLI., S. 121), and of Schultz in 1845 (Journ. fur Prakt. Chem., Bd. XXXIV., S. 61-63, 1845), upon the evolution of oxygen from waters containing animalculæ and 'green plants,' under the influence of sunlight, were confirmations of some of the experimental results of Count Rumford. present, oxygen will be given out and immediately expelled, until the maximum of the solvent power for air by the given temperature be attained. 4th. On the withdrawal of sunlight and the reduction of the temperature, the animalculæ cease to evolve oxygen, and that which is in solution becomes the prey of the decaying organic matters present. 5th. The hydrogen of organic bodies (as Liebig has remarked) oxidates first. This position I have verified by a series of observations, to which I will here only refer. "The following experiment may be mentioned in this connection. Two clear glass globes of about four and a half inches in diameter, filled with waters from two wells in Cambridge, in one of which, after rest of twelve hours in leaden pipe, lead was detected, and in the other of which, after equal exposure, no lead was recognized, were placed in a window of south-southeast exposure. Into each globe a skein of silk weighing 1.25gr. was introduced; at the end of five days, the quantity of gas evolved was more than twice as great in that containing the wellwater that acted on lead as in the other. No admeasurement of the quantity was attempted, for the following reason: I wished to know what would become of these gases, the water containing organisms which must soon consume their supply of nutriment. In a period equal to the above, the gases were entirely absorbed, and after the lapse of a month, during which time there were several days of brilliant sunshine, no gases appeared. An isolated experiment of this description cannot have much value. But it seemed to me worth recording, as sustaining what Liebig has remarked, that of the elements of organic bodies the hydrogen is more readily oxidated than the carbon, and as illustrating the decay of organic bodies in water. "Of the various popular reasons why lead should not be employed for distributing water, the following have been found not to be sustained by experiment or authority. "1. The Galvanic Action of Iron and Lead. The effect of con tact with iron, in most of its points of view, has been investigated. In diluted acids, bright lead in contact with iron is positive, coated lead, negative. YORKE. - Diluted acid facilitates the solution of iron in contact with lead. RUNGE. In strong nitric acid, iron, in connection with lead, is positive. DELARIVE. In potash solution or lime-water, bright lead is positive to iron, but oxidated or coated lead is negative. This is also true of these metals in a solution of saltpetre. YORKE. — It is also true in a solution of sal-ammoniac. WETZLAR. Thus in acid, al kaline, and saline solutions, - all the conditions in which Cochituate water can occur, — iron, if not at first, will, after a short interval, be the metal at whose expense the galvanic action will be sustained. "2. The Action of Iron-Rust. It was natural to suppose that the moist iron-rust flowing from the mains into the leaden pipes might, by reduction to a lower oxide, promote the oxidation and solution of lead. Bars of lead in contact with hydrated peroxide of iron, in open tubes, containing Cochituate, Croton, Jamaica, Fairmount, Albany, and Troy water, arranged on the 15th of May, gave, when tested on the 17th, 22d, and 27th of May, and 7th of June, with ferrocyanide of potassium, no indication of protoxide. The same water in which nails were immersed, tested from time to time, gave occasional evidence of the presence of protoxide of iron. I placed peroxide of iron and bright bars of lead in flasks of distilled and Cochituate water, and sealed them, on the 7th of last June. The flasks are in my possession still, and though the air was expelled only so much as boiling five minutes would accomplish, the bars of lead are quite as undimmed as on the day they were sealed up. It is scarcely necessary to state that the iron rust, in actual service, does not come in contact with lead, but with the suboxide, or other coat.* "3. The Solubility of the Suboxide of Lead. I have been unable to procure the slightest trace of lead in water deprived of its air, after long contact with the suboxide of lead. Mitscherlich remarks of its insolubility.t "4. The Action of Alkaline Chlorides upon Lead, in the Absence of Oxygen or Atmospheric Air. The following experiment was made and several times repeated by me with graduated solutions of common salt. A flask of one gill capacity, containing a quantity of lead shavings, presenting an extent of surface comparatively great, was one third filled with a solution of common salt. This flask was connected by a tube, bent twice at right angles, with a cup of mercury. The cork, tube, and neck, at the connections, were carefully covered with sealing-wax, that the flask might be air-tight. So arranged, the flask * Reference has been made to the experiments of Napier upon this point. He made no experiments with peroxide of iron, but with neutral salts of the peroxide, and he states distinctly that lead exposed to them a little while became coated, and that action was thereafter arrested. - Lond., Edinb., and Dubl. Philos. Mag., May, 1844, pp. 365–370. + Lehrbuch der Chemie, 2te Band, S. 511. |