518 
DR. PLAYFAIR ON THE NITROPRUSSIDES, A NEW CLASS OF SALTS. 
Quadribasic prussides, Fe 2 Cyg+4R, formula of ferrocyanides. 
Tribasic prussides , . . Fe2Cyg+3R, formula of ferridcyanides. 
Bibasic prussides .... Fe 2 CygH-2R, formula of undescribed compounds. 
With regard to the last class, its existence must be yet considered hypothetical, but 
in searching for it, I have received sufficient encouragement to enable me to hope 
that I shall very shortly be able to establish it. Without presenting the analytical 
evidence to this effect, it can only be adduced as a probable hypothesis to explain 
the nitroprussides. The latter class of salts may be supposed to correspond to a bi- 
basic class of prussides in which part of the cyanogen is replaced by nitrous oxide. 
Thus 5(Fe Cyg-I-R) = Fcg Cyig + 5R correspond to 1 equiv. of a nitroprusside, 
Fcg Cyi 2 3NO-I-5R. The great approximation of the latter formula to the more 
simple expression Fe 2 Cyg NO-{-2R, renders it singular that the small deficiency of 
carbon refuses to allow the formula to be thus expressed. In such a case this sup- 
posed bibasic prusside and the nitroprusside would stand in a very simple relation : 
Fe2Cyg^ +2R, 
Fe 2 CygNO-l-2R. 
The complicated formula required by the analyses of all the nitroprussides might 
be resolved into 2 (Fe 2 Cyg NO-{-2R)H-(Fe Cy 2 NO-fR), in which the latter member 
is constituted on the same type, but more cyanogen is displaced by the nitrous oxide. 
It will not excite surprise, after what has been learned in the previous inquiry as to 
the obstinate manner in which the nitroprussides unite with cyanides from which they 
are not removable by any means tried, that a salt constituted on the same type should 
unite with the true nitroprussides and form an integrant conjugate compound which 
is not broken up by crystallization. It appears therefore very probable that the true 
formula of the nitroprussides may in reality be Fe 2 Cyg NO-(-2R, and that further re- 
search may eliminate this compound. Hitherto this has not been done, and the only 
formula which correctly expresses the analysis is Feg Cyi 2 3NO-1-5R, which on theo- 
retical, but on no other grounds, may be resolved into 
2(Fe2 Cyg NO-f 2R)-l-(Fe CygNO+R). 
I trust soon to be able to present to the Society another memoir on the prussides, 
which will confirm experimentally some of the views theoretically supported in the 
present communication; but at present I submit the previous results with a view of 
drawing attention to this interesting class of salts, and with a perfect conviction that 
future research will simplify and explain the remarkably complex and unsatisfactory 
formulse which I have been obliged to adopt, without believing them to be the 
correct expression of the constitution of the salts. 
