Three notions have been submitted to the public in the last twenty years in regard to the nature of muriatic acid. First, the gas detached from common salt by sulphuric acid has been thought to be the acid in a state of purity, and constituted of a certain base or radical united to oxygen; this was the notion inculcated in the articles alluded to above. Second,—it is stated as a fact that when oxymuriatic acid and hydrogen in equal volumes are united by the electric spark, a volume of muriatic acid gas is the result equal to the sum of both the other volumes, and that this gas perfectly agrees with the gas obtained from common salt by sulphuric acid; this suggested the idea that muriatic acid gas is a compound of what has been called real or dry muriatic acid one atom, and water one atom. And, third, it is argued, that the element we have called oxymuriatic acid gas, is, for aught that appears, a simple body, and consequently, that muriatic acid gas is the real acid, and is constituted as above, of one atom of hydrogen, and one atom of oxymuriatic acid (now called chlorine.) It is not intended here to enter into a discussion of the arguments and facts adduced in support of the different conclusions. More experience must be had before all the doubts and difficulties are removed from the subject. But it will be proper to illustrate these different positions by an example. For instance, common salt, muriate of soda or chloride of sodium. By the first notion 50 parts of dry common salt will consist of one atom of muriatic acid gas, 22, and one atom of caustic soda, 28. By the second notion the same salt will be formed of 30 parts of muriatic acid gas, and 28 of caustic soda; but 8 parts of water evaporate when the salt is dried. By the third view common salt consists of oxymuriatic acid, or chlorine and sodium, or the metal of which caustic soda is the protoxide; and 50 parts of salt will consist of 29 chlorine and 21 sodium, or one atom of each.
NITRIC ACID—COMPOUNDS OF AZOTE AND OXYGEN.
Since the account of nitric acid (Vol. 1, page 343) was printed, a change has universally taken place in estimating the weight of the nitric acid atom, and of the proportion of azote and oxygen in the same. This has been effected chiefly by a more correct analysis of nitre than existed at that time. Nitre is now found to consist nearly of 52 parts acid and 48 parts potash per cent. Hence if the atom of potash be 42, that of nitric acid must be 45; for, 48 ∶ 52 ∷ 42 ∶ 45, nearly. That is, the nitric acid atom consists of 10 azote + 35 oxygen by weight; or of 2 atoms of azote (according to my estimate) and 5 of oxygen. There appear to be two nitrous acids; namely, the one which I have designated by that name, which may now be called subnitrous, or as Gay Lussac terms it pernitrous; and the other what I considered as nitric acid in the former volume, composed of 1 atom azote, and 2 of oxygen.
Real nitric acid then is that combination which is effected by uniting oxygen with a minimum of nitrous gas; or 1 measure of oxygen with 1.3 nitrous gas, (See Vol. 1, page 328). The oxynitric acid, which I was led to infer from the last mentioned combination, (1 azote with 3 oxygen) does not appear to exist. The Table of nitric acid (Vol. 1, page 355) will require some correction. An increase of about 4 per cent. should be made, I apprehend, on the quantities of acid corresponding to the several specific gravities.
Since my former volume of Chemistry was printed, several essays on the compounds of azote and oxygen have been published, with some new and some additional experiments, the chief of which may be seen in Sir H. Davy’s Elements of Chemical Philosophy, the Annales de chimie et de physique, Vol. 1; Annals of philosophy, Vol. 9 and 10; and the Manchester Society’s Memoirs, Vol. 4, second series; also Dr. Thomson’s first principles of Chemistry. Notwithstanding all that has been written on the subject, there still appears uncertainty as to the number of combinations formed by these two elements, their relative weights, and the number of atoms in the several compounds.
The results of an experiment I lately made on the decomposition of nitrate of potash by heat seem to be worthy of record, as I am not acquainted with those of any other person who has pursued the experiment to the same extent.—I took an iron retort of 6 cubic inches capacity, and cleaned it as well as I could from carbonaceous matter which it had previously contained, first by heating nitre to redness for an hour or more in it, and then washing it repeatedly with water till the liquid came out tasteless, and only mixed with a little red rust; I then put in 480 grains of purified nitre, and having secured a copper tube to the retort so as to be air tight, the retort was put into a fire and gradually raised to a red heat, and the fire was occasionally urged with a pair of bellows, in order to keep up a glowing red on the retort for nearly two hours; the air was received over water in jars; the first 4 or 5 inches were thrown away, and the rest was preserved and transferred to a graduated jar; the products were examined in successive portions as under, namely,
| Inches. | |||||||
| 1 | produce, | 85 | cubic inches, | 83 | per cent. pure | = | 70.5 |
| 2 | 5 | 77 | = | 3.85 | |||
| 3 | 25 | 50 | = | 12.5 | |||
| 4 | 6 | 30 | = | 1.8 | |||
| Total | 121 | Oxygen | 88.65 | ||||
| Oxygen | 88.65 | = 30 grains. | |||||
| Residue | 32.35 | = 10 grains. | |||||
About 1 per cent. on the whole gas was carbonic acid, the rest oxygen and azote, the weights of which would be nearly as above.
Towards the last the gas came very slowly, and being of inferior quality, the operation was discontinued.
The remaining contents of the retort were diluted with water, and well washed till the water ceased to shew alkali; the liquid was then concentrated and gave 1600 water grain measures of the sp. gr. 1.153. There were obtained also 64 grains of red oxide of iron from the washing of the retort, containing 19 grains of oxygen.