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without addition, give out more or less of thissulphuretted hydrogen, and thus are decom-posed partially or entirely. The hydro-sul-phuret of magnesia is compleatly decomposedat this heat; that of lime almost entirely ; thehydrosulphurets of potash or soda are partiallyso, and become very alkaline, but still retain somuch sulphuretted hydrogen as to give it outabundantly on being heated with sulphur.

The hydrosulphuret of ammonia is depositedin the form of needle-shaped crystals, by passingequal portions of sulphuretted hydrogen andammoniacal gas into a dry vessel cooled by iceexternally. This hydrosulphuret of ammonia isat first colourless, but soon turns yellow whenexposed to the air, and then by partial abstrac-tion of the hydrogen contains an excess ofsulphur relatively to the hydrogen. It is alsovery volatile, and sublimes even in a commontemperature to the top of the vessel in which itis kept, and thus it may be obtained separate fromthat portion which has undergone partial de-composition.

The sulphuretted hydrosulphuret of ammoniahas an oily consistence when saturated withsulphur, which is efFected merely by digestingsulphur with Boyle’s fuming liquid (or hydro-sulphuret of ammonia) at a common tempera-tuse. When this is diluted with water, muchsulphur is precipitated, even if liquid ammoniabe previously added. This saturated sulphur-etted hydrosulphuret l of ammonia gives outvapours in the air, but much Jess than Boyle’sliquid ; which latter will give out a very densevapour for a long time when exposed to oxygen,but scarcely any in azote or hydrogen.

SULPHUREOUS ACID. _

When sulphur is burnt in a given quantity ofdry oxygen gas, the sole product is sulphureousacid gas. Some condensation always takes place,but it is variable, and in small quantity whenthe sulphur is the purest. It therefore is mostprobably owing to some hydrogen remaining inthe sulphur, so that if sulphur were quite pure,it would probably be converted into sulphureousacid gas by oxygen without any change of bulk.Therefore, by ascertaining the weight of a givenvolume of sulphureous acid gas, and deductingfrom it the weight of an equal bulk of oxygenthe remainder will he the sulphur. Thus 100cubic inches oLsulphureous acid gas weigh at amean pressure and temperature 6 8 grains, andICO cubic inches of oxygen gas weigh 34 grains,leaving also 34 for the weight of the sulphur.Ilcnce it is most probable that sulphureous acid

gas is composed of equal weights of sulphur andoxygen, and the absolute weight of each in agiven quantity of the acid gas, is equal to thatof the same volume of oxygen.

Another proof of the constitution of sul-phureous acid is obtained from the combustionof sulphuretted hydrogen in Volta’s eudiometer.*This compound contains exactly its own bulk ofhydrogen, and 100. cubic inches consist (asabove mentioned) of 34.23 grains of sulphur,and 2.27 grains of hydrogen. Now when sul-phuretted hydrogen is exploded with abundanceof oxygen, the products are sulphureous acidgas and water; and 2 measures of sulphurettedhydrogen require 3 measures of oxygen for thispurpose, or 100. require 1.50. of oxygen. There-fore, according to the well known constitutionof water, the 100. cubic inches of hydrogen(contained in the same bulk of sulphurettedhydrogen) require 50. cubic inches of oxygen toproduce water, which would leave 100. cubicinches of oxygen, weighing about 34. grains, toform sulphureous acid with 34.23 grains of sul-phur, which are nearly equal weights.

Professor Berzelius ascertains the compositionof sulphureous acid from the sulphate of barytes,as mentioned in the article Affinity in this ap-pendix, which gives the component parts of thisacid to be 100. of sulphur, and 97.83 oxygen.These differ but little from being equal parts ofeach.

SULPHURIC ACID.

Much information has been lately given byexperimental researches on the constitution ofthis most important acid, and the theory of itsformation. It has long been known that themost concentrated acid which can he obtainedin a separate state, contains a considerablequantity of water in its composition, which maybe expelled when it enters into chemical unionwith any base, a fixed alkali for example, andit is on this principle that Mr. Kirwan formedhis tables for the proportions of real acid inliquid sulphuric acid of different degrees of di-lution. Sulphuric acid therefore is composedof sulphur, oxygen, and water, the latter ofwhich it is capable of giving up when it entersinto combination with a base.

•• The proportion of oxygen to sulphur in sul-phuric acid appears by a variety of experimentsto be 1-t times as much as that in sulphureousacid, and in thel&tter'it is'as already mentioned,nearly, if not exactly, equal to the sulphur. Sothat if 30 grains of sulphur take 30 grains ofoxygen to become sulphureous acidj it will

a Daltyu’s System, vol. ii.