No. 6.] HARRINGTON— NOTES ON DAWSONITE. 300 



No. I. to warrant tlie conelusiou that the mineral is constant m 

 composition. They arc as follows : 



II. 



Carbonic acid 30.73 



Alumina with traces of Fcg O3 , 32.68 



Lime , 5.65 



Magnesia , 0.45 



Soda 20.1 7 



Water [10.32] 



100.00 



lu this analysis the total alkaline chlorides are calculated as 

 soda, the amount of potash not having been determined. 



In No. 1 the excess of carbonic acid above that required to 

 form neutral carbonates with the bases other than alumina is 

 10.69 ; while in II. it is 11.46. This excess must either be 

 in combination with the alumina, or else must 2;o towards form- 

 ing bicarbonates with a portion of the protoxide bases. If the 

 alumina is not present as carbonate, we might then suppose it to 

 exist as hydrate. There is, however, not sufficient water to 

 form trihydrate, the compound known in nature as Gibbsite, and 

 too much to form the monohydrate or diaspore. Native tri- 

 hydrate, moreover, is only soluble in acids with difficulty, and 

 diaspore is insoluble, unless after ignition. 



The amount of vvater is about that which would be required 

 to form dihydrate, — a hydrate which, as prepared in the labora- 

 tory, is soluble in acetic acid, though insoluble in the stronger 

 acids. But hydrochloric, or nitric acid, readily dissolves all the 

 alumina in the Dawsonite. 



The crystalline character of the mineral, and the uniformity 

 of its optical and chemical characters, forbid its being regarded 

 as a mechanical mixture ; and, for the present, we can only say 

 that it may be a hydrous carbonate of alumina, lime and soda, 

 or perhaps a compound consisting of a hydrate of alumina com- 

 bined with carbonates of lime and soda.^ 



If we adopt the former view, and consider that alumina may 

 exist in combination with carbonic acid, we need no longer con- 

 sider Hovite as a bicarbonate of lime, but may adopt the sugges- 

 tion of the Messrs. Gladstone, that it is a double carbonate of 

 alumina and lime. 



* There is nearly enough carbonic acid to form neutral carbonate 

 with the lime, and bicarbonate with the soda, 



