18S Experiments to determine the [Sept. 



those whose acute angles are truncated. When examined by a 

 lens, a facet is seen on the smaller edge of the rhomb, forming with 

 its flat face an angle of about 10°. 1 endeavoured to ascertain the 

 angles of the crystals by Wollaston's goniometer; but the plates 

 were so minutely thin, that no light could be seen reflected on the 

 outer edges. As far as my eye enabled me to judge, on comparing 

 them with different lines, the angles of the rhomboidal plates are 

 about 12(>° and 54°, and those of the six-sided laminas about 126°, 

 143°, and 91°. The length of the largest crystals never exceeds 

 ^th of an inch ; the surface is very brilliant ; they are perfectly 

 transparent and colourless ; but when viewed by transmitted light, 

 appear of various prismatic colours. Exposed to heat, they melt 

 and dissipate in air, a smell of sulphurous acid being exhaled. 



Examination of the Gaseous Product. 



As much of the gas as could be collected was received in vessels 

 in the mercurial trough ; and it is to be observed, that all the 

 experiments hereafter detailed were performed over mercury. 

 Knowing that a considerable quantity of oxygen was present in the 

 gas, my first endeavours were to detect its amount ; but to my 

 great astonishment, not the least trace of its presence was discover- 

 able by any of the usual tests. With nitrous gas no red fumes 

 weve produced, but a very slight whitish cloudiness, faintly per- 

 ceptible, appeared, which afterward condensed on the sides of the 

 vessel. The mixture was reduced in volume when equal portions 

 were combined, the diminution amounting to 11-94 per cent, of 

 the whole. Detonated in Volta's eudiometer by itself and with 

 hydrogen, at repeated intervals, no explosion would ensue. Exa- 

 mined in Hope's eudiometer with a solution of the sulphureted 

 bydrosulphuret of potash, an absorption of about 40 per cent, took 

 place; but this was evidently condensed by the water of the solu- 

 tion, as water itself was found to absorb the same quantity. 



The gas was now examined for hydrogen. In Volta's eudiometer 

 with hydrogen, no explosion was produced on sending several 

 shocks through it. Allowing the mixture to stand for a day, and 

 then repeating the discharge, an explosion immediately took place; 

 the amount of whose diminution indicated the presence of 42*42 

 per cent, of hydrogen in the gas. In the residue, after its absorp- 

 tion by water, there is found a portion of hydrogen amounting only 

 to iS-fJl per cent, in the gas employed: and in the residuum, after 

 it* action on the metallic salts, hydrogen is found in variable quan- 

 tities, amounting on an average to about 36 per cent, in volume of 

 the original gas. The cause of this variation in the appearance of 

 hydrogen in the gas will be accounted for in the sequel. The gas 

 reddens infusion of litmus, and a portion of it combines with 

 alkalies, earths, and metallic oxides. This portion, therefore, 

 possesses most decided characters, while all the residuum appears 

 to be azote only. 1 he gas, then, is seen to consist of an acid gas; 

 a quantity of hydrogen gas that appears intimately combined with 



