On Crystallography, 349 



Let us suppose, for example, that the absoUue charejeof 

 the areometer, including the body which ought to serve as 

 the means of fixing the substance, being also ^20 grannnes, we 

 iiiust have been under the necessity of placing 16 grammes 

 beside the body which we wish to weigh, in order lo produce 

 the levelling oace more. We shall have four grammes 

 for the weight of this body. Let us afterwards suppose 

 that, the same body being dipped in water, we liad still 

 added six grammes to the 16 which were already in the 

 upper cistern, which makes in all 22 grammes. These 

 SIX grammes will represent the weight of the volume of 

 water displaced, and the proportion will be 6 : 4 : : 1 ; x, 

 which will give 0'66G6 for the specific gravity of the body 

 subjected to the experiment. 



in effect, if the weight of the body of an equal volume 

 was exactly the same with the weight of the water, it would 

 be necessary to charge the upper cistern with 20 grammes 

 onlv, as at first, whert the body would be phniged in the 

 water, because it would perform the office of the volume 

 of water displaced. But we have seen that in this case 

 the upper cistern was charged with 22 grammes, from 

 which it«follows that there remains to the water an effort 

 of two grammes, besides that of four grammes, which it 

 employs in sustaining entirely the body. The total force 

 therefore of the water is equivalent to six grammes ; or, 

 what comes to the same thing, the weight of a volume of 

 water equal to that of the body is six grammes. Tims the 

 specific gravity of the water is lo that of the body in the 

 ratio of six lo four, as vve have seen above. ' 



Water always has a trifling adherence to the areometer, 

 which is such that this instrument loaded with the same 

 weight may rem^vn a little more or a little less deeply plunged 

 in the water. In order lo get rid of the trifling uncertainty 

 which arises from this variation in the level, having allowed 

 the areometer lo attain the state of stability, raise it a little 

 above its position, and afterwards &iuk it a little below it 

 by abandoning it every time to itself; and if the scratched 

 line is between the two points which are levelled, you may- 

 conclude that the upper basin has its true charge. 



We may instead of distilled water employ rain-water, 

 which at the same temperature has visibly the same den- 

 sity. In the event of our only wishing to dispel a doubt 

 whether a mineral might be referred to one species more 

 than lo anv other, we should have a sufficient approxima- 

 tion on operating with river- or well-waier, rh^ tenjperature 

 of which should differ in a few degrees oniy froip that 

 which had been chosen for arranging the table of specific 



gravities. 



