VII. To the stop-cock of the upper cylinder of the mercurial airholder, a capillary tube was adapted, bent so as to be capable of introduction into an orifice in the stopper of a graduated phial similar to that employed for mingling acids with water, and sufficiently long to reach the bottom. With another orifice in the stopper of the phial was connected a similar tube curved, for the purpose of containing a fluid, and of increased diameter at the extremity.[29]
50 cubic inches of pure nitrous gas[30] were thrown into the mercurial apparatus. The graduated phial, containing 90 grains of nitric acid, of specific gravity 1,5, was placed on the top of the airholding cylinder, and made to communicate with it by means of the stop-cock and first tube. Into the second tube a small quantity of solution of potash was placed. When all the junctures were carefully cemented, by pressing on the airholder, the nitrous gas was slowly passed into the phial, and absorbed by the nitrous acid it contained; whilst the small quantities of nitrogene evolved, slowly drove forward the solution in the curved tube; from the height of which, as compared with that of the mercury in the conducing tube, the pressure on the air in the cylinder was known.
In proportion as the nitrous gas was absorbed, the phial became warm, and the acid changed color; it first became straw-colored, then pale yellow, and when about 7½ cubic inches had been combined with it, bright yellow. It had gained in weight nearly 3 grains, and was become of specific gravity 1,496.
This experiment afforded me an approximation to the real difference between nitric and yellow nitrous acid; and learning from it that nitric acid was diminished in specific gravity by combination with nitrous gas, I procured a pale acid of specific gravity 1,504.[31] After this acid had been combined in the same manner as before, with about 8 cubic inches of nitrous gas,[32] it became nearly of specific gravity 1,5, and had gained in weight about 3 grains.
Assuming the accuracy of this experiment as a foundation for calculation, I endeavoured in the same manner to ascertain the differences in the composition of the orange colored acids, and the acids containing still larger proportions of nitrous gas.
93 grains of the bright yellow acid of 1,5 became, when 6 cubic inches of gas had been passed through it, orange colored and fuming, whilst the undissolved gas increased in quantity so much as to render it impossible to confine it by the solution of potash. When 9 cubic inches had passed through, it became dark orange. It had gained in weight 2,75 grains, and was become of specific gravity 1,48 nearly. Hence it was evident that much nitrous gas had passed through it undissolved. 25 cubic inches more of nitrous gas were now slowly sent through it: it first became of a light olive, then of a dark olive, then of a muddy green, then of a bright green, and lastly of a blue green. After its assumption of this color, the gas appeared to pass through it unaltered, and large globules of fluid, of a darker green than the rest, remained at the bottom of the cylinder, and when agitated, did not combine with it. The increase of weight was only 1 grain, and the acid was of specific gravity 1,474 nearly.
In this experiment it was evident that the unabsorbed nitrous gas had carried over with it a considerable quantity of nitrous acid. I endeavoured to correct the errors resulting from this circumstance, by connecting the curved tube first with a small water apparatus, and afterwards with a mercurial apparatus; but when the water apparatus was used, the greater part of the unabsorbed gas was dissolved with the nitrous acid it held in solution, by the water; and when mercury was employed, the nitrous acid that came over was decomposed, and the quantity of nitrous gas evolved, in consequence increased.
As it was possible that a small deficiency of weight might arise from the red vapor given out during the processes of weighing and examining the acid in the last experiment, 35 cubic inches of nitrous gas were very slowly passed through 90 grains of pale nitrous acid, of specific gravity 1,5: it became of similar appearance to that just described, had gained in weight 6,75 grains, and was become of specific gravity 1,475.
These experiments did not afford approximations sufficiently accurate towards the composition of deoxygenated acids, containing more nitrous gas than the dark orange colored. To obtain them, a solution consisting of 94,25 grains of blue green, or perfectly nitrated acid, (if we may be allowed to employ the term), of specific gravity 1,475, was inserted into a graduated phial, and connected by a curved tube, with the mercurial airholder; in the conductor of which a small quantity of water was inserted to absorb the nitrous acid which might be carried over by the gas. Heat was slowly applied to the phial, and nitrous gas given out with great rapidity. When 4 cubic inches were collected, the acid became dark olive, when 9 dark red, when 13 bright orange, and when 18 pale. It had lost 31 grains, and when completely cool, was of specific gravity 1,502 nearly. The water in the apparatus was tinged of a light blue; from whence we may conclude that some of the nitrous gas was absorbed by it with the nitrous acid: but it will be hereafter proved that the orange colored acid is the most nitrated acid capable of combining undecompounded with water, and that the color it communicates to a large quantity of water, is light blue. If then we take 6,1 grains, the quantity of gas collected, from 31 the loss, the remainder is 24,9, which reasoning from the synthetical experiment, may be supposed to contain nearly 3 cubic inches of nitrous gas. Consequently, 94,25 grains of dark green acid, of specific gravity 1,475, are composed of nearly 21 cubic inches, or 7,2 grains of nitrous gas, and 87,05 grains of pale nitrous acid, of 1,504.
VIII. Comparing the different synthetical and analytical experiments, we may conclude with tolerable accuracy, that 92,75 grains of bright yellow, or standard acid of 1,5, are composed of 2,75 grains of nitrous gas, and 90 grains of nitric acid of 1,504; but 92,75 grains of standard acid contain 85,23 grains of nitrous acid, composed of about 27,23 of oxygene, and 58, nitrous gas: now from 58, take 2,75, and the remainder 55,25, is the quantity of nitrous gas contained in 90 grains of nitric acid of 1,504; consequently, 100 grains of it are composed of 8,45 water, and 91,55 true acid, containing 61,32 nitrous gas, and 30,23 oxygene; or 27,01 nitrogene, and 64,54 oxygene: and the nitrogene in nitric acid, is to the oxygene as 1 to 2,389.