ed. In the short account of hyponitrous acid which I have How obtain. given in the first volume of this work (p. 127), I have stated that it does not seem capable of existing except in combination with a base. However, M. Dulong has shown that this opinion is not well founded. He mixed together 4 volumes of deutoxide of azote, and 1 volume of oxygen gas, and exposed the mixture to the cold produced by a freezing mixture, it condensed into a deep green liquid, exceedingly volatile, and losing the liquid state when the cold was withdrawn. Now as deutoxide of azote is a compound of equal volumes of azote and oxygen without any condensation whatever, it is evident that this green liquid was a compound of 2 volumes azotic gas, 3 volumes oxygen gas, or (which is the same thing) of 1 volume azotic and 11⁄2 volume oxygen gas. This is equivalent to which is the composition of hyponitrous acid. Thus it appears from Dulong's experiment, that hyponitrous acid is capable of existing uncombined with a base. This acid when in contact with air mixes with it and becomes a red vapour, which is not again condensible without the application of an intense cold. When this acid is mixed with water it undergoes a partial decomposition. Deutoxide of azote is given out with a strong effervescence, and there remains a solution of nitric and hyponitrous acid in the water. The same decomposition takes place when we attempt to combine this acid with a base. But it is easy to obtain hyponitrites by double decomposition. The manner of proceeding is to boil a mixture of nitrate of lead and metallic lead in water; a dihyponitrite of lead is formed. If this hyponitrite be mixed with Chap. I. Unites with other acids. the requisite proportion of bisulphate, the oxide of lead and the sulphuric acid will unite and form an insoluble powder, while the hyponitrous acid will unite with the base to which the sulphuric acid was united, and form a hyponitrite which will dissolve in the water. We may also convert nitre into a hyponitrite by raising it to an incipient red heat, and keeping it for some time in that state. And several other nitrates may be converted into hyponitrites by a similar process. This acid has the curious property of combining with several other acids, especially with sulphuric acid. If we pass a mixture of four volumes deutoxide of azote and 1 volume of oxygen gas through concentrated sulphuric acid, we obtain a crystalline mass composed of sulphuric acid, hyponitrous acid, and water. When gently heated it melts, but becomes again solid on cooling. Its specific gravity is 1831. When heated a little higher than 270° it undergoes decomposition, deutoxide of azote is disengaged, leaving a mixture of sulphuric and nitric acids. The nitric acid cannot be expelled by distillation, probably from want of water, without which that acid cannot exist in a separate state. When the crystalline mass is thrown into water deutoxide of azote is disengaged. When sulphurous acid, deutoxide of azote, and oxygen gas are mixed, the crystals do not appear unless water be at the same time present. According to the analysis of Henry,* this crystalline mass is composed of 4 atoms sulphuric acid 4 atoms water 1 atom hyponitrous acid 20 4.5 4.75 29.25 If we suppose the hyponitrous acid to unite with half of the sulphuric acid, the remainder will consist of 1 atom sulphuric acid united to two atoms water, which is the combination of that acid and water of most easy congelation. Is it to this that we are to ascribe the state of crystallization which the double acid assumes? 3. Nitrous Acid. In the first volume of this work (p. 128), I have given an account of the method of procuring nitrous acid from nitrate of lead, and likewise its properties and composition as determined by Dulong. What is called fuming nitric acid, contains a conAnnals of Philosophy (2d series), xi. 368. siderable quantity of nitrous acid. If we distil such an acid Two different opinions have been advanced respecting the nature of nitrous acid. The greater number of chemists consider it as a peculiar acid, composed of 1 atom azote Class L. Div. I. 4 atoms oxygen But it is destitute of the property of combining with bases; no such class of salts as nitrites existing. On this account Berzelius considers it as a compound of And has given it the name of acidum nitrosonitricum. It is obvious that this view of its composition will come to the same thing, as far as the ultimate elements are concerned. For nitric acid being a compound of 1 atom azote and 5 atoms oxygen, and hyponitrous acid of 1 atom azote and 3 atoms oxygen, it is clear that if we combine them together we have a compound containing History. which is the composition deduced from the analysis of Dulong. As nitrous acid does not combine with bases, it is a matter of indifference which of these views we adopt. SECTION IV.—OF THE ACIDS OF CARBON. There are two acids at present known, composed of carbon and oxygen, namely, carbonic acid and oxalic acid. 1. Carbonic Acid. Carbonic acid exists ready formed in prodigious quantity in the mineral kingdom, constituting an essential constituent of carbonate of lime, which, under the names of marble, limestone, and chalk, occurs so abundantly in almost every part of the earth. It exists also in great abundance in carbonate of iron; while carbonate of barytes, strontian, magnesia, lead, copper, bismuth, and zinc, occur also in greater or smaller quantity in the mineral kingdom. It is given out also in great abundance by active volcanoes, and many springs in different parts of the earth are impregnated with it. It is formed also abundantly by the burning of wood and pit coal, and by the breathing of animals. The existence of this substance as an essential constituent of limestone, was first demonstrated by Dr. Black, who gave to carbonic acid the name of fixed air, because it exists in a fixed state in these mineral bodies. Its properties were first investigated by Mr. Cavendish. Mr. Keir, from a knowledge of these, first concluded that it was an acid, and gave it the name of calcareous acid. Bergman adopted the same opinion in 1774, and gave it the name of aerial acid.*. Mr. Bewdly called it mephitic acid, because it cannot be respired without occasioning death. Finally, Lavoisier, after proving it to be a compound of carbon and oxygen, gave it the name of carbonic acid, which has been long in universal use. I have already given an account of the properties of this acid in the first volume of this work (p. 161). The salts which it forms with bases have received the name of carbonates. It is by no means a powerful acid, being expelled by the greater * Opusc. i. 1. number of the oxygen acids. As is the case with weak acids it has the property of uniting with the different bases in two, and frequently in three proportions. This acid has been shown to be a compound of 1 atom carbon 2 atoms oxygen and its atomic weight is 2.75. 2. Oxalic Acid. 0.75 2.00 2.75 Class I.' Div. L. As the earliest and best account of the oxalic acid was pub- Discovery. lished by Bergman, he was for a long time reckoned the discoverer of it; but Mr. Ehrhart, one of Scheele's intimate friends, informs us, that the world is indebted for its knowledge of this acid to that illustrious chemist, and Hermbstadt and Westrumb assign the discovery to the same author.+ The assertions of these gentlemen, who had the best opportunity of obtaining accurate information, are certainly sufficient to establish the fact, that Scheele was the real discoverer of oxalic acid. This acid exists, ready formed, in the vegetable kingdom, sometimes in the state of binoxalate of potash, as in oxalis acetosella and common sorrel; and sometimes in the state of oxalate of lime, as in the root of rhubarb and of many other plants. I have given a short account in the first volume of this work (p. 172), of the methods of preparing this acid. It may be procured also from the binoxalate of potash, by dissolving the salt in hot water, and adding carbonate of potash as long as any effervescence takes place. Then add a solution of acetate of lead, as long as a white precipitate continues to fall. Collect the precipitate, wash it and dry it. For every 181⁄2 parts of this powder add 6-125 parts of strong sulphuric acid, pre-, viously diluted with ten times its weight of water, and digest the mixture for some time. The sulphuric acid will unite with the oxide of lead and form an insoluble powder, while the oxalic acid being disengaged will remain in solution. Separate the sulphate of lead, and concentrate the solution till the oxalic acid crystallizes. Oxalic acid thus obtained is in transparent or translucent Properties. crystals, which have usually the form of flat tables, consisting in reality of six-sided irregular prisms. Mr. Brooke has shown * Elwert's Magazine for Apothecaries, 1785, part i. p. 54. |