APPENDIX F. — CHEMICAL ANALYSES. 421 



the crystals was heated to drive off the water of crystallization. 

 Having previously learned that it was an alum, with the double 

 base of manganese and alumina, I made a careful analysis and ob- 

 tained the following result from the salt dried by blotting paper : — 



100 grammes of the freshly crystallized salt gave — 



Water 73.0 



Protoxide of manganese 08.9 



Alumina 04.0 



Sulphuric acid 18.0 



It is not easy to explain the relation of the acid to the two bases 

 here in accordance with the usual constitution of alums, as there 

 does not seem to be enough acid for the supply of an equivalent to 

 each base, nor of alumina for the manganese. But as I have not 

 the time to repeat my experiments, they must stand for what they 

 are worth. 



This salt may be substituted for common alum in nearly all its 

 various uses for tanning, in combination with the salt brine of the 

 Great Salt Lake, in what is called the process of tawing; and 

 where tan bark is difficult to obtain, it is a valuable acquisition to 

 the arts. And should the locality of alum at any time give out 

 from exhaustion, the rock may be blasted and the alum made by 

 artificial means, as the alum slates of England are worked. 



The manganese alum is also susceptible of various uses as a 

 mordant and a colouring agent in dyeing, where it is not only a 

 substitute for common alum, but subserves other and additional 

 purposes of communicating various tints of fancy colours to shades 

 of red, brown, &c. Thus we have purples, lilacs, browns, and 

 many other tints, from the use of manganese. 



For details in this art, see Parnell's Applied Chemistry— Calico- 

 printing. 



Yours truly, 



L. D. Gale. 

 Howard Stansbury, Esq. 



Captain Corps of Topo graphical Engineers, JJ. S. Army. 

 Washington, March 25, 1851. 



