296 Mr. Porrett on Ferro-chyazate of Potash, [Oct. 



perceived that in the formula which I had proposed as represent- 

 ing the atomic constitution of the ferro-chyazate of potash, the 

 only part which did not appear to be supported by the results of 

 experiment, was that which gave the quantity of iron as amount- 

 ing to one atom, all my experiments, as well as those of Dr. 

 Thomson, having made it less ; and Mr. Phillips's message 

 seemed to prove that these experimental results were much 

 nearer to the truth than the theoretical ones. 



I, therefore, felt the necessity of making further researches 

 into the very complicated composition of this salt, convinced 

 that the uncommon difficulties which its analysis presents, had 

 never yet been so completely overcome as to admit of its con- 

 stituents being stated with that rigid accuracy which is now so 

 essentially required in chemical investigations. 



I began with experiments to ascertain the quantities of iron 

 and of potash which the salt contains ; and after trying various 

 modes of analysis, I fixed upon the following, as being sus- 

 ceptible of greater accuracy than any other which I had 

 attempted. 



Twenty-five grains of ferro-chyazate of potash were burned in 

 a covered platina crucible with nitrate of ammonia; after the 

 combustion, which was very vivid, I found in the crucible a 

 saline mass mixed with red oxide of iron, which weighed 21 "5 

 gr. and was composed of 17 gr. of nitrite of potash, and 4*5 gr. 

 of red oxide of iron : I separated the nitrite of potash from the 

 oxide of iron by lixiviation, and added a sufficient quantity of 

 muriatic acid to it to convert it into a muriate; nitrous gas was 

 immediately given off; and after evaporating to dryness, I 

 obtained 16 - s gr. of chloride of potassium ; these quantities of 

 red oxide of iron and of chloride of potassium are equivalent to 

 1042 potash, and 3*15 iron, which, multiplied by 4, give 41*68 

 of the former, and 12-6 of the latter substance, as contained in 

 100 of the ferro-chyazate. 



The quantity of alkaline base in the salt being thus ascer- 

 tained, and also the ferruginous portion of the acid, I had next 

 to find the quantities of the other constituents of that acid ; 

 namely, its carbon, azote, and hydrogen ; and for this purpose, 

 I repeated several times the combustion of the salt, mixed with 

 peroxide of copper: the average quantity of gases collected from 

 one grain of the salt, with from 20 to 30 times its weight of per- 

 oxide, was as follows : 



Cubic inches. Volumes. 



Carbonic acid 1*79 4 



Azote 0-45 1 



2^24 5 



a result which exactly corresponds as to the proportions between 

 the two gases with what I before published, but which differs 



