k 



i. 



fc. 



p 



«f 



I 



if 



I 



+>-' 



»rj 



i 



1-v 



Sect. VIII.] 



mi:, ^ralogy. 



23 



These characters may be regarded as aids towards the 

 approximate knowledge of a mhieral, and as such may be 

 useful, more especially to one who may in the first in- 

 stance be desirous of availing himself, with as little loss 

 of time as possible, of the differences or resemblances of 



an 



f T 



to 



minerals he may have collected, endeayomnng 

 refer them to known substances, so that while opportunl 

 ties may continne to bo afForded he might institute stil 



further search for any minerals respecting which it may 



1 



be desirable to collect additional information. 



Supposing the voyager in possession of minerals col- 

 lected on some excursion, he will find it useful to try 



their 



gravi 



be sufficiently calm for the purpose. This is no difficult 

 task, and the use of the needful apparatus for the purpose 

 is soon acquired.* As the specific gravity of minenils, 



* Much may be done with tlie common balance made for the purpose, 

 -ftdiercby, after 'weighing the body in the air, it is weighed in the water, 

 which should be distiUed water, and enough can be got by dexterously 

 condensiDg the steam coming out of a common tea-kettle. 



For very exact determinations a flask of the kind herewith represented 

 is used, c (i is a ground-glass stopper, made so 

 exactly to fit, that its bottom coincides with the 

 line a h, so that the volume of the interior of the 

 flask is constant, A capillary tube traverses the 

 stopper through its length, so that when the flask 

 is filled any excess of water escapes through this 



tube. The flask full of water is first weighed, 



and then the weight of tlie mineral is taken in 



the air. The mineral is then placed in the flask, 



so that it remains full, after the volume of water 



equal to that of the substance inserted has 



escaped. If now the fiask, with the mineral in 



it, be weighed, the difference of weight gives that of the volume of water 



disjdaced, and by finding the relation of the weight of the mineral to 



that of the water, the specific gravity is obtained. If the substance tried 



ff* 



m 



'-iC\-^ 



>- 



y*' * 



