130 J. H. Pratt — Northwpite^ Pirssonite^ 



The chemical composition of this mineral differs from gay- 

 lussite, CaCOg.Na^COg.SH^O, in having only two instead of five 

 molecules of water of crystallization. Experiments that were 

 made to determine at what temperature the water is driven off 

 from the air-dry powder are as follows : 



Loss. 



Six hours at 100° Nothing 



Ten hours at 150° 13-85 



Three hours at 200° .37 



Six hours at 250° _. -36 



Below faint redness '16 



Total 14''74 



As practically all of the water is expelled below 150°, it 

 must be regarded as water of crystallization. 



In analysis I the water was weighed directly by the method 

 described by Penfield,* and in II it was determined by loss 

 on gentle ignition. 



Pyrognostics. — The mineral decrepitates, when heated 

 before the blowpipe, and fuses about 2 — 2*5, coloring the 

 flame intensely yellow. It reacts alkaliue after heating. In 

 the closed tube it decrepitates and gives off water at a low 

 temperature. It is soluble in cold dilute hydrochloric and 

 nitric acids with effervescence. 



Name. — The author takes pleasure in naming this mineral 

 jpirssonite^ in honor of his friend and associate. Prof. L. Y. 

 Pirsson, of the Sheffield Scientific School. 



Gayhtssite. 



The only reference that the author has been able to find to 

 gaylussite from this region is in an article by IIanks,f who 

 mentions the mineral as occurring in crystalline masses, but not 

 in distinct crystals. There must have been some mistake in 

 identification, however, for as pointed out by Pirsson, J the 

 reactions which are ascribed to the mineral are impossible ones 

 for a compound with the chemical composition of gaylussite. 



According to information received from Mr. Northup, the 

 gaylussite occurs abundantly at this locality. It is found in 

 many parts of the deposit and at varying depths. All of the 

 specimens that have been supplied by Mr. JSTorthup have, 

 moreover, been distinct crystals. 



Crystallization. — The forms that have been observed are as 

 follows : 



h^ 010 m, 110 e, Oil 



c, 001 5, 101 r, 112 



*This Journal, xlviii, p, 31, 1894. 



f MiniDg and Scientific Press, Mar. 26, 1892. 



iZs. Kr., xxiii, p. 504, 1894. 



