126 J. H. Pratt — J^orthupite, Pirssonite, 



The ratio of the CO, : CI : M^O : I^a^O is almost exactly 

 !,v 2:1:1: 1*5. Two-thirds of the sodium, if taken to form a mole- 



1 cule of Na^COg, would leave just enough to form with the 



chlorine a molecule of E"aCl. This would then give as the 



formula, MgCO,, JSTa.CO,, :N'aCl. 



The percentage composition required by this formula is 



given below, together with the results of the analysis recalcu- 

 '■ lated to 100 per cent, after deducting the slight amounts of 



water and insoluble material and converting a sufficient amount 



of the soda into metallic sodium to unite with the chlorine 

 ^ and form NaCl. 



fi Calculated for 



' Found. MgCOa . Na^COs . NaCl. 



'■ CO, 35-43 35-41 



MgO 16-22 16-09 



: ]Sra,0 24-90 24-96 



' ' CI ... 14-23 14-28 



Na 9-22 9-26 



100-00 100-00 



Pyrognostics. — Before the blowpipe, the mineral fuses at 

 1, with frothing, due to escaping carbon dioxide, and yields a 

 white or grayish white mass, which reacts alkaline with mois- 

 ened turmeric paper. The flame is colored intensely yellow. 

 In the closed tube, the mineral decrepitates violently, some- 

 times giving ofi a trace of water, derived probably from 

 impurities held mechanically in the crystals. The crystals are 

 easily soluble in cold dilute hydrochloric and nitric acids with 

 effervescence. Cold water acts slowly on the mineral, but hot 

 water decomposes it very rapidly with separation of magne- 

 sium carbonate. 



Name. — The name, northupite^ was given to this mineral by 

 Mr. Foote as a compliment to Mr. ISTorthup, whose very care- 

 ful search has brought to light a number of interesting min- 

 erals from this locality. 



Pirssonite^ a New Mineral. 



As stated in the introduction, a new mineral was first 

 observed by Mr. Northup among some crystals of gay-lussite, 

 which it somewhat resembles. It has been found very spar- 

 ingly in only one boring, '' JSIew Well," which also furnished 

 the northupite crystals. With the two exceptions mentioned 

 under northupite, only detached crystals have been observed, 

 and they were probably formed in the same part of the 

 deposit which yielded the northupite. Unfortunately, pirsson- 

 ite must be classed among the rare minerals ; but it is hoped 



