1816.) Experiments on Rrussic Acid 359 
dity. ‘To, form,an idea ,of its constitution, we may .compare “it to 
sulphureted hydrogen. But this mobility is only relative; 1t depends 
on the circumstances.in, which the acid is placed. cf 
1en this acid is kept in well-closed vessels, eventhough no,air 
he present, it is sometimes decomposed in less than an hour. I 
have often kept it 15 days without alteration; but it is seldom that 
it can be kept longer, without exhibiting signs of decomposition. It 
begins by assuming a reddish-brown colour, which becomes deeper 
and deeper, and it gradually deposites a considerable carbonaceous 
matter, which gives a deep colour both to water,and acids, and 
gives out a strong smell of ammonia. Af the bottle; containing the 
prussic acid be not hermetically sealed, nothing remains but a.dry 
charry mass, which gives no colour to water. 
To know exactly the xresults,of this decomposition, I introduced 
prussic acid into a barometrical tube well -freed from air, and waited 
till the inside of the tube was coated with.a charny covering, which 
rendered it opake. ‘The height at which the mercury stood was jin- 
considerable; but.on inclining the tube, the mercury filled it, which 
shows that no gas was extricated. On Wing up the tube, I recog- 
nized the odour of prussic acid. Water introduced acquired a strong 
brown colour. Potash and lime disengaged ammonia from it, and 
sulphuric acid rendered the odour of prussie acid very sensible; but 
no carbonic acid was disengaged. From this it is evident that by the 
decomposition of prussie acid a portion of ammonia is formed, which 
combines with the remaining prussic acid. ‘The charry substance 
naust of necessity contain a quantity of azote; for ammonia being 
composed of three volumes of hydrogen and one of azote, while 
prussic acid contains equal volumes of these two elements, two-thirds 
of the azote must remain with the carbon, and form of consequence 
an azoturet of carbon, 
Phosphorus and iodine, being yolatilized in prussie vapour, did not 
appear? to produce any alteration. Sulphur treated in the same way 
absorbs it readily, We obtain a solid compound of sulphur and 
prussic acid, which I consider of the same nature as that formed by 
sulphureted hydrogen and the radical of prussic acid, of which I 
shall speak afterwards. I postpone, likewise, the examination. of 
the compound formed by chlorine and prussic acid. , 
Among the simple metallic bodies, potassium is one of those 
whose action is most proper to throw light on the true nature of 
prussic acid, When heated in prussie vapour mixed with hydrogen 
or azote, there is absorption without inflammation, and the metal is 
converted into a grey spongy substance, which melts, and assumes a 
yellow colour, Supposing the quantity of potassium employed 
capable of disengaging from water a volume of hydrogen equal ta 
50 parts, we find, after the action of the potassium, 
_1. That the gaseous mixture has experienced a diminution of 
Tolyme amounting to 50 parts : 
_ 2, On treating this mixture with potash, and analyzing the re- 
‘sidue by oxygen, that 50 parts of hydrogen have been produced : 
