A NEW CLASS OF SALTS. 
513 
In such a variable compound as this, close results can scarcely be looked for in 
two analyses. As an approximation, however, it will be seen that the iron is to the 
sodium as 5 ; 8, and to the sulphur as 5 : 3. 
The blue unchanged compound gives with protosulphate of iron a beautiful pre- 
cipitate of the same purple blue colour as itself, but this is decomposed by washing. 
With salts of lead it gives a brownish yellow precipitate, with salts of copper a brown 
precipitate, both these being obviously products of decomposition. 
28. The purple blue compound dissolved in water speedily becomes red, and when 
in this state, a salt of lead throws down a pinkish red precipitate. This red solution 
however soon decomposes, a brownish precipitate falling, and the yellow colour due 
to a prusside being seen in the solution. If the sulphide originally employed con- 
tained sulphuretted hydrogen, a soluble prussian blue is also found in the liquid. 
During these changes, ammonia, hydrocyanic acid, and a gas possessing the proper- 
ties of nitrogen are given off. In fact, on mixing the solutions of sulphide and nitro- 
prusside, it is difficult, even by keeping the solutions quite cold, to prevent the form- 
ation of a little ammonia and escape of nitrogen. The solution of the purple com- 
pound in water decomposes even under the air-pump, depositing the brown precipi- 
tate, and it does so immediately when it is boiled. 
When the solution is filtered from the brown precipitate, the addition of alcohol 
separates ferrocyanide of sodium. The alcoholic filtrate strikes a blood-red colour 
vdth a persalt of iron, and with sulphuric acid evolves nitric oxide, which is immedi- 
ately rendered sensible by a protosalt of iron, a nitrite being thus shown to be in 
solution. Ammonia cannot be detected in the solution, neither does it appear to any 
great extent when the transformation takes place in the cold, though it always does 
so when ebullition is used to hasten the transformation. It therefore appears to be 
the product of an after action. 
The brown precipitate is first to be examined. It is found to consist of peroxide 
of iron and sulphur, the latter remaining when the former is dissolved out by an acid. 
It was analysed by oxidation with nitromuriatic acid. 7*21 grs. gave 16‘90 grs. 
sulphate of barytes, equal to 2’33 grs. of sulphur, and 4'22grs. peroxide of iron, the 
rest being water. Hence the proportion of sulphur to iron in equivalents is nearly 
as 4:3 ; the proportion for 2‘33 sulphur would yield 3’0 iron, while 2'95 was found 
by the experiment. 
It was now desirable to ascertain what proportion of iron was thrown down as 
ferrocyanide and how much remained in the brown precipitate. For this purpose a 
portion of a preparation, which had become green by standing in the air-pump, was 
first analysed in order to ascertain the relative proportion of its constituents, and it 
was then dissolved in water and boiled. 
14*41 grs. gave 6*93 grs. sulphate of barytes, 17‘68grs. gave 3*55 grs. peroxide of 
iron and 10*00 grs. sulphate of soda. 6*025 grs. gave 3*31 grs. carbonic acid and 
