18 PHILOSOPHICAL TRANSACTIONS. [ANNO 179& 



I afterwards distilled 100 grs. of the yellow oxyde of iron, mixed with 200 grs. 

 of sulphate of ammonia. Pure ammonia first came over, and afterwards some 

 sulphureous acid. When the retort began to melt I removed it, and found the 

 iron chiefly in the state of red oxyde, or colcothar, mixed with some sulphate of 

 iron. When oxyde of zinc was used, the residuum was sulphate of zinc. 

 Minium, when triturated with sulphate of ammonia, immediately decomposed 

 it like lime, or the alkalies, and when distilled, the retort contained sulphate of 

 lead. When native green oxyde of copper was distilled with sulphate of ammo- 

 nia, the residuum was partly red oxyde of copper, with some sulphate of the 

 same. But the ammonia came over in a concrete state, by reason of the car- 

 bonic acid contained in the green oxyde. The oxydes therefore of iron, zinc, 

 lead, and copper decompose the sulphate of ammonia by combining with 

 the acid. 



I next mixed it with the yellow tungstic acid ; but after the distillation, I found 

 the tungstic acid unchanged, excepting that it had acquired a tinge of pale 

 green. The ammonia and the sulphureous acid also came over in the same 

 manner as when only the sulphate of ammonia was distilled. Lastly, I distilled 

 1 oz. of the sulphate of ammonia with 20 grs. of the yellow molybdic acid. 

 During the distillation, the ammonia and sulphureous acid were produced in as 

 great quantities as when the sulphate of ammonia was distilled by itself. But 

 the molybdic acid remained in the retort, deprived of oxygen, in the form of a 

 black blistered matter, which was again converted into the yellow acid when dis- 

 tilled with nitric acid. 



From these experiments it appears, that the sulphate of ammonia is not, as 

 many eminent chemists have imagined, incapable of being decomposed without 

 some intermediate substance, but on the contrary, the whole of it can be raised 

 and a great part decomposed, whenever a proper degree of heat is applied; for 

 then a certain portion of ammonia first comes over, so that the remainder is 

 combined with acid in excess, and the hydrogen of the ammonia which remains 

 unites with part of the oxygen of the sulphuric acid, and forms water, which 

 passes into the receiver, accompanied by the acid, now become sulphureous acid, 

 and by the azote in the state of gas. Various methods have long been in use 

 to decompose ammonia. Metallic oxydes produce this effect; and Scheele par- 

 ticularly mentions, that if arseniate of ammonia is distilled, gas is produced, 

 and the acid of arsenic is reduced to the metallic form, and as such is sublimed*. 



appears, a vacuum takes place, occasioned by the alkaline gas, which previously filled the vessels, 

 being neutralized by the sulphureous gas, which is then produced. It is necessary therefore, in about 

 10 or 15 minutes after the commencement of the operation, that the fire should be raised, and the 

 azotic gas will then soon begin to pass into the jar. Some water will most commonly rush into the 

 receiver, but if the capacity of this is not too small, there will not be time enough for the water 

 to rise sufficiently high, so as to pass into the retort.— Orig. 



* Essays, page 155. The same effects were also produced when acid of arsenic was sublimed 

 with muriate of ammonia, p. l6l.— Orig. 



