86 THE CANADIAN NATURALIST. [Vol. X. 



If from the above analyses we deduct the substances which 

 may justly be regarded as impurities, including lime and mag- 

 nesia in the form of carbonates, and then calculate the normal 

 constituents for one hundred parts, it will be seen that the re- 

 sults agree well with the formula Na2 [AI2] CgOg + 2H2O: 



I II III IV Formula. 



Carbon dioxide* 29.27 27.96 29.06 27.78 30.49 



Alumina 37.88 36.42 36.70 36.12 35.55 



Soda • 20.19 22.41 22.65 22.86 21.48 



Water 12.66 13.21 11.59 13.24 12.47 



It has also been suggested that the formula may be written 

 SCN.^COa) + (AI2C3O9) + 2(He[Al2jOe).t 



According to Friedel, the Tuscany Dawsonite when heated to 

 180° C. loses nothing but a little hygrometric water. Like the 

 Canadian mineral it gives up both its " carbonic acid " and water 

 at a red heat. The calcined residue also dissolves easily in 

 hydrochloric acid. Neither the hardness nor the specific gravity 

 of the European variety has been ascertained. For the Canadian 

 mineral the original determinations were, H = 3, G = 2.40. 



* The atomic ratios for I and II are as follows : 



C 665 .636 2 



[AI2] 369 .355 1 



Na 651 .723 2 



2.764 2.696 8 



Q 2 I 703 .734 2 



f Am. Jour. Sci. III. xxii. 157. 



