1819.]. Mr. Porrett on Sulphuretted Chyazic Acid. 363 
the quantity of sulphur which he employed ; the other consists 
in first expelling by a moderate heat all the water of crystalliza- 
tion from the ferruretted chyazate ; the sulphur then combines 
quietly with the salt immediately on fusion with it; and with 
these proportions there is no great excess of sulphur remaining. 
I have endeavoured to acquire some idea of what passes in this 
operation, and have ascertained that 10 gr. of ferruretted chya- 
zate of potash combine with 4 gr. of sulphur, and give off 1°35 gr. 
of water, and 0°5 of a grain of mixed gas and vapour, measuring 
at mean temperature and pressure 0°3 of a cubic inch, half of 
which was absorbable by water, to which it gave the smell of 
sulphuret of carbon, and the rest may have been carburetted 
fatcaee ; but an accident prevented any particular examination 
of it. The residuum weighed 12°15 gr.; it was composed of 
sulphuretted chyazate of potash, of sulphuret of iron, and of a 
solid compound of charcoal with sulphur: hence it appears pro- 
bable, that in this experiment the ferruretted chyazic acid, which 
I have before shown to be a compound of four atoms carbon, one 
of azote, two of hydrogen, and one of tron (Annals of Philosophy, 
vol. xii. 1818), relinquishes half its carbon and hydrogen, with 
the whole ofits iron, and takes two atoms of sulphur in exchange, 
the liberated carbon and iron at the same time combining with 
sulphur. 
I beg to add to this communication, as being closely connected 
with the subject, the results of a slight and not very precise 
examination, which I made some time since, of the yellow crys- 
tals, which Gay-Lussac discovered were formed when cyanogen 
and sulphuretted hydrogen gases are mixed together over 
mercury: I have remarked that these crystals are not formed 
when the two gases are quite dry, but that they are quickly pro- 
duced if a drop of water is passed up into the mixture. The 
colour and the nature of the crystals obtained do not appear to 
me to be always the same ; they are sometimes greenish-yellow, 
and soluble in water; at other times they are orange-brown, and 
only partially soluble therein: I believe that the former are 
produced when the cyanogen employed is only 2ds the volume 
of the sulphuretted hydrogen ; and that the latter make their 
appearance when the volume of cyanogen exceeds that of 
the sulphuretted hydrogen; however this may be, the aqueous 
solutions, after the separation of the brown deposit from the 
orange-coloured crystals, appear identical in their chemical 
characters. This solution possesses none of the properties of 
sulphuretted chyazic acid; it does not change the colour of 
litmus; it has no effect on solutions of iron, nor on other me- 
tallic solutions, with the exception of those of gold, silver, 
palladium, and mercury, in which it produces brown and 
grey precipitates ; it contains neither prussic nor sulphuretted 
ehyazic acid; yet this latter acid is formed in it when it is first 
