104 M. Vogel on [Frs. 
Ipassed the vapour of the acid through a red hot porcelain tube, 
and obtained at the furthest extremity of it, sulphur, sulphuretted 
chyazic acid undecomposed, and prussic acid, which was partly 
saturated with ammonia. But I found no charcoal in the tube; 
though I have no doubt that if the acid be passed very slowly 
through a red hot tube, it will be completely decomposed, and 
will deposit charcoal. 
When the acid is passed through a red hot porcelain tube 
filled with iron turnings, we obtain sulphuret of iron, prussic acid, 
and sulphuretted hydrogen. 
Sulphuretted chyazic acid crystallizes in six-sided prisms at 
the temperature of 541°. 
Action of Air. 
When pure concentrated acid is exposed to the air in an open 
vessel, it soon begins to evaporate. A slip of paper, with which 
the mouth of the vessel was covered, became red; while the 
acid assumed a yellow colour, and deposited sulphur.* 
Mr. Porrett states that the acid becomes red on the contact 
of air, and that it is oxydized ; but I cannot adopt his opinion. 
The red colour doubtless proceeded from some protoxide of iron _ 
which had passed into peroxide by the contact of the air, or it 
might, perhaps, have been occasioned by the contact of paper, 
or other organic bodies floating about in the air. The sensibi- 
lity of this acid for peroxide of iron is so great that it cannot be 
filtered through paper, or placed in contact with cork, without 
becoming red. 
Action of Chlorine. 
When sulphuretted chyazic acid was mixed with liquid chlorine, 
this last substance lost its odour and its yellow colour. The 
mixture was now precipitated by muriate of barytes, which was 
not the case before. Hence sulphuric acid had been formed ; 
but no sulphur was deposited. 
Neither does chlorine precipitate sulphur from the sulphuret- 
ted chyazate of potash ; though M. Grotthuss has founded a 
mode of analyzing this acid upon the separation of the sulphur 
in this case. I have already shown that the sulphuretted on 
zate of potash, procured by Grotthuss, by means of a red heat, 
contained sulphuretted hydrogen. This was the reason why 
chlorine precipitated sulphur from it. 
Sulphuretted chyazic acid is completely decomposed, when 
agitated with chlorine ; for the mixed liquid, after being satu- 
rated with potash, is no longer reddened by persulphate of iron. 
But prussian blue is formed, which is insoluble in muriatic acid. 
When a.mixture of sulphuretted chyazic acid and chlorine is 
sl'ghtly heated, a very distinct odour of prussic acid becomes 
perceptible, If this vapour is made to pass into lime water, we 
* When exposed in small bottles to the rays of the sun, it becomes likewise 
yellow, and deposits sulphur, 
