Dr. Kane on the Compounds of Ammonia. 81 



two equivalents of a magnesian protoxide, with oxide of kalium, or ammonia and 

 water. This family was discovered by Klauer, who formed double sulphates of 

 alumina with the protoxides of iron and nickel, with magnesia and oxide of zinc ; 

 and lately one of the most remarkable examples of this class, a double sulphate 

 of alumina and protoxide of manganese was found forming a thick bed on the 

 coast of Africa, and brought to this country, where it has been analyzed by 

 Apjohn and by myself. 



The general formula of this class, as has been accurately determined with 

 the manganese and zinc members, is as follows : ro =^ protoxide, 



1 . (ro . SO3 . ho) -\- (A^^Og + 3 SO3) -J- 24 HO, 



resembling accurately 



2. (ho . SO3 . ukd) -\- {Al.p.j -{- 3 SO3) 4" 24 HO, 

 which it further assimilates itself to in taste and solubility. 



The relation of the water of these alums to heat is very remarkable, and 

 indicates very accurately the nature of their constitution. Thus by a temperature 

 of 212°, eighteen equivalents of water are lost; by a heat of 300° there are 

 given out six more ; but the expulsion of the remaining equivalent requires a 

 temperature equal to the melting point of lead, indicating the intenseness of the 

 power with which it is retained ; in fact the zinc alum may be looked on as com- 

 posed of ordinary sulphate of zinc and ordinary sulphate of alumina, 



zno . SO3. HO-]- 6ho 



A4O3.3SO34- 18ho 



zno . SO3 . HO -f- A/2O3. 3SO3 + 24ho. 



The form mwo . SO3. ho-}- 6ho is not the ordinary condition of proto-sulphate 

 of manganese, but it also can be obtained with that quantity of water. 



The preceding considerations showing, with considerable probability, that 

 two equivalents of an oxide of the magnesian class may replace in combination, 

 and even affect isomorphism with an equivalent of the alkaline group, it may be 

 proper to inquire how far evidence capable of illustrating the theory under 

 examination can be collected from amongst the numerous species of minerals 

 which are supposed to present cases of replacement of an alkali by an earth. In 

 such cases the substitution may take place in two ways, which renders the 

 demonstration of its occurrence much more difficult than it might at first be 



VOL. XIX. M 



