Dr Turner's Chemical Examination of Tahasheer. 3S7 



The density falls below the number observed by Mr Jar- 

 dine, but agrees closely with the observations of Mr Macie and 

 Mr Cavendish. 



Tabasheer is very slightly affected by heat. When heated to 

 212° Fahr. it gives out both air and water, and the latter has 

 neither an acid nor alkaline reaction. The loss in weight is 

 small, and differs slightly in the different specimens. Thus 

 the chalky tabasheer loses 0.838 per cent., the translucent 1.62, 

 and the transparent variety 2-411 per cent. On exposure to 

 the atmosphere it absorbs both air and moisture, and speedily 

 recovers its original weight. At a red heat all the varieties 

 become dark in a slight degree, but almost instantly recover 

 their former appearance ; a minute quantity of smoke accom- 

 panied with an empyreumatic odour rises at the same time, 

 and the moisture which is expelled has an acid reaction. 

 These phenomena are owing to the decomposition of a trace 

 of vegetable matter. By being thus heated to redness the 

 chalky variety loses 1.277, the translucent tabasheer 3.84, and 

 the transparent tabasheer 4.518 per cent. The whole loss oc- 

 casioned by a red heat is not recovered by exposure to the air. 



Tabasheer feds gritty in the mouth, and causes a sensation 

 very like magnesia, but with a rather nauseous taste. It is 

 brittle and easily reduced to powder. When boiled in distil- 

 led water it yields to that menstruum only a trace of vegeta- 

 ble matter. Digested with muriatic acid, moderately diluted 

 with water, the solution on being evaporated left a minute re- 

 sidue, which deliquesced on exposure to the air, and proved 

 to be muriate of lime. The chalky tabasheer by this treat- 

 ment lost 0.4, and the translucent tabasheer 0.3 per cent, of 

 lime. The transparent variety yielded' barely a trace of any 

 thing to muriatic acid. 



Tabasheer dissolves readily in a solution of pure potash, 

 even after being heated to redness. The alkaline solution of 

 the chalky kind is slightly turbid, but that of the other varie- 

 ties is quite transparent. On neutralizing with muriatic acid, 

 and evaporating to dryness to render the silica insoluble, a 

 quantity of that earth is left almost exactly equal to the quan- 

 tity originally employed. The filtered liquid contained no- 



