232 Penfield and Pratt — Occurrence of 



extracted, while relatively only a very small proportion of the 

 calcium was dissolved, a result which would not have taken 

 place if the alkalies had belonged with the thaumasite. A 

 small quantity of alkali sulphate may, therefore, be regarded 

 as impurity, and deducting from the analysis the alkalies and 

 sufficient SO, (0*64: per cent) to convert them into sulphates, 

 and recalculating to one hundred per cent, the following results 

 are obtained, which agree satisfactorily with the values required 

 by theory : 



By recalculation. Theory. 



Si0 2 9-38 9-64 



C0 2 ... 6-90 7-08 



SO, 12-95 12-86 



CaO 27-47 27-01 



HO. 43-30 43-41 



100-00 100-00 



Hoping to obtain data concerning the constitution of the 

 mineral, experiments were made to determine the temperature 

 at which the water was driven off. As determined by Lind- 

 strom, the mineral slowly loses water at 100° C, and in our 

 experiment, after heating for over ninety hours, a loss of 29 '35 

 per cent was obtained, but the weight had not become con- 

 stant. At 150° the weight soon became constant and then at 

 200°, 250° and 300° respectively constant weights were obtained, 

 and in each case the heating was continued until the loss of 

 weight during several hours did not amount to more than a 

 few tenths of a milligram. Between 300° and 360° no loss of 

 weight was obtained, but the material still contained water 

 which, as seen by a closed tube experiment, was expelled at 

 much below a red heat. 



The results obtained from -6663 grams of the air-dry min- 

 eral are as follows : 



Proportional parts 

 Loss. using -^ of total 



H 2 as unity. 



Two days in dessicator Nothing 



Nine hours at 150° 37*41 13-13 



Seven hours at 200° 1 -82 0*64 



Eight hours at 250° 1'41 0'50 



Five hours at 300° _ 1*05 0-37 



Below redness 1-08 0-38 



Total 4277 



It is evident from the above that 13 molecules are to be 

 regarded as water of crystallization and two molecules, suffi- 



