406 Dr. Forchhammer on a Salt composed of [June, 



posely for the experiment, I have perfect reliance on their indi- 

 cations. The sraallness of the apparatus and its extreme sim- 

 plicity, render the determination of the point wherever it is to 

 be placed, a very plain matter. This I submit to those who are 

 capable of availing themselves of the means it affords, and who 

 are qualified for appreciating its powers. 



James Crichton. 



Article II. 



On a Salt composed of Sulphuric Acid, Peroxide of Iron, aud 

 Ammonia. By Dr. Forchhammer. 



(To the Editor of the Annals of Philosophy.) 



DEAR SIR, Copenhagen, Jpril 8, 1823. 



Having prepared a solution of gold by means of nitric acid 

 and muriate of ammonia, and precipitated the gold by protosul- 

 phate of iron, in order to determine whether any further por- 

 tion of gold might be obtained by evaporation, the solution was 

 concentrated to the consistence of a syrup, and suffered to 

 remain for a month, when beautiful octohedral crystals of a wine 

 yellow colour were formed on the sides of the vessel. It first 

 occurred to me that this salt might be a peculiar compound of 

 sulphuric acid and peroxide of iron ; but I soon discovered that 

 it also contained ammonia, and that it was an alum in which 

 peroxide of iron supplied the place of alumina. 



This salt is soluble in about three times its weight of water at 

 60°, and, by repeated crystallization, it may be obtained per- 

 fectly colourless ; the regular octohedron is the most usual form 

 of this salt, and although the cubo-octohedron sometimes occurs, 

 I never obtained any perfect cubes. 



Fifty parts of this salt were dissolved in water, and precipi- 

 tated by nitrate of barytes, 5033 of sulphate of barytes were 

 obtained, containing 17-298 of sulphuric acid = 34-596 per 

 cent.* 



One hundred parts of the salt were dissolved in water, and 

 decomposed by ammonia, the precipitate was digested during 24 

 hours in a solution of soda, and this, upon the addition of muriate 

 of ammonia, deposited slight traces of alumina, which increased 

 by ebullition, and weighed, when dry, 026 part. In another 

 experiment, from 60 parts of the salt, 0*19 of alumina was 

 obtained. The oxide of iron after being redissolved in muriatic 



a 



* In this and die following calculations, the proportions are given from Berzelius's 

 tables (Stockholm, 1818). If the more simple numbers of Dr. Thomson are adopted, 

 the result differs very little from that deduced from Herzeljus's numbers. 



