348 On Crystallography* 



areometer*. Let us suppose that the weights employed 

 form a sura of t20 grammes. This is tlie chargcof the 

 areometer, which can only serve for bodies the weight of 

 which does not exceed 20 grammes. 



Having taken out the chariic, put the stone into the same 

 cistern, and place beside it the weights necessary for level- 

 ling the areometer. Supposing these last weights to b« 

 equivalent to 3*6 grs. subtracting this number from 20, 

 we shall have 64 grs for the weiirht of the stone in the air. 

 Withdraw the areometer, in order to place the stone in 

 the lower bason E; then having redippcd the instrument^ 

 add into the cistern A the weights necessary for producing 

 the level once more. Let us suppose these additional 

 veirhis to be equivalent to 2*48 grs. This is what the 

 Stone has lost of its weight in the water, and at the same 

 time is-the weight of an equal volume ot water. 



Make this proportion : 2'4S grs. or the weight of 

 the volume of water equal to that of the stone is to 6*4 

 grs. the absolute weight of the stone, as the unity which 

 represents in general the specific gravity of tiie water is to 

 a fourth term, which will be the specific gravity of the 

 stone f. This fourth term taken with four decimals is 

 2^5S0d. Now on running over the table of specific gra- 

 vities, we fmd that that of water sapphire answers to nearly 

 the same number, while that of the oriental sapphire is 

 about 4. The stone subjected to the experiment is there- 

 fore a quartz only. 



If we wished to weijih a substance respectively lighter 

 than water, it would be necessary, on placing it in the 

 lower basin, to fix it steadily to it. In this case the body 

 which serves to fix it is considered as forming part of the 

 areometer. In other respects the operation is the same as 

 in the preceding case 5 only the second terra' of the pro- 

 portion is smaller than the first, which is necessary; smce 

 the fourth term, which gives the specific gravity of the 

 body, ought to be also smaller than the third, which repre- 

 sents the specific gravity of the water. 



♦ VCe raay fairly dispense with this operation, because, we are under-- 

 stood to know before-haiid, from a prior experimeiu, the weight neces- 

 sary for levelling the arec-mctcr : it is Ix'st liowcvtr to repeat th s ope- 

 ration every time, on account of the small dtflerencea which may happen iu 

 the tetnpcrature, or in the qnality of the liquid. 



f It is more natural to employ unity in order to designate the specific 

 gravity of the water, which is* tiie lerm of comparison to which we refer a!) 

 the spiK-ific gravities of other bodies, thrin to represent it hy 10(X) or by 

 J0,0l''<^ as is generally done. To conclude, the calculation i» the same, 

 except that we have generally a decimal fraction in the result. 



Let 



