100 Mr. Everitt on preparitig Hydrocyanic Acid from 



not taken, it was greenish. Perhaps M. Gay Lussac poured 

 strong sulphuric acid on the powdered crystals, when a very 

 complicated change takes place. (See Thomson, 7th edition, 

 vol. ii. p. 251.) M. Gay Lussac also states, that after making 

 a few experiments on the new salt, the results appear {'' sem- 

 blent" showing that he trusted more to the pen than the ba- 

 lance,) to lead to the consequence that it is a compound of 9 

 cyanogen, 7 iron, and 2 potassium ; so that supposing we have 

 enough of the original ferrocyanuret of potassium to yield 14? 

 proportions of potassium, 7 of iron, and 21 of cyanogen, then by 

 boiling with sulphuric acid, 7 proportions of iron, + 2 potas- 

 sium + 9 cyanogen fall, 12 of cyanogen go off* as hydrocyanic 

 acid, and 12 of potassium are dissolved by the sulphuric acid. 

 Now, I prove by {b.) that the relation of the potassium dis- 

 solved by the sulphuric acid to that precipitated is as 3 : 1, 

 and not as 6: 1; by (c.) that the relation of the cyanogen dis- 

 engaged as hydrocyanic acid is to that in the precipitate as 

 1:1, and not as 12 : 9. And the quantity of yellow salt pro- 

 duced in («.) serves to confirm both the above results. 



The theory of the subsequent conversion of the salt into 

 Prussian blue by moistening it with dilute sulphuric acid and 

 exposing it to air is consequently unknown. I have not yet 

 examined the precise change which takes place with sufficient 

 care to give an opinion: that potassa is dissolved out, and that 

 the action of free oxygen is essential to the change, is certain. 



(5.) Had I examined Gay Lussac's paper before I began 

 my experiments, his high authority would have made me con- 

 sider any further experiments on this subject as useless; but 

 as I had finished the experiments marked Nos. 1 and 2, before 

 I saw his paper, I was induced to repeat my experiments with 

 redoubled care : hence the series No. 3, and hence their nearer 

 approach to the calculated numbers. I must therefore con- 

 clude that M. Gay Lussac has operated on the salt obtained 

 by the action of concentrated sulphuric acid on the crystals. 

 The change in that case, according to Thomson, is so com- 

 plicated that sulphurous gas, ammonia, carbonic oxide, azote, 

 are given off'. I doubt if any definite conclusions can be drawn 

 from it. 



(6.) The best proportions, therefore, of the ferrocyanuret 

 of potassium and sulphuric acid to be used when we want hy- 

 drocyanic acid are as follows. To every 212*47 grains of the 

 crystals dissolved in about 2 fluid ounces of water, add so 

 much dilute sulphuric acid as shall contain 120 grains of real 

 acid, and by conducting the distillation carefully, 41 grains of 

 hydrocyanic acid pass off", and that I find with the first Jrd of 

 the water: of course water must be put into the receiver and 



