256 Description of an Universal Hydrometer 



has been preferred for the bulb of this instrument, on ac- 

 count of its more readily dividing the fluid in its passage tip 

 and down ; and the size of it is such, that half a pint of 

 any liquid is sufficient for trial with it. 



The hydrometer (see Plate IX.) consists of the bulb h, a 

 small stem a c, with a cup d on its top to receive weights, 

 and a shank ef beneath the bulb with a pointed screw, to 

 which is affixed a cup g, to receive weights or solids when 

 their specific gravities are required to be taken. 



The instrument is accompanied with an accurate set of 

 grain weights. 



The weight of the hydrometer itself is 700 grains, and dh 

 adding 300 grains in the upper cup, and immersing it in 

 distilled water, at the temperature of 60 degrees, Fahr. 

 it will subside to the middle mark on the stem, and will 

 then consequently displace 1000 grains of water. 



It follows, therefore, from this adjustment of the bulk of 

 the instrument, that each grain in the upper cup will re- 

 present one thousandth part of the specific gravity of the 

 water, or one unit in specific gravity, if that of water be 

 taken to be 1000 ; and one-tenth of a grain one-tenth of 

 unit, which is also the value of each of the small divisions 

 on the stem ; and accordingly, when the hydrometer is im- 

 mersed in any liquid until it sinks to the middle point on 

 the stem, the specific gravity of such fluid will be indicated 

 by the sum of the weight of the instrument (which is, as 

 before stated, 700 grains) and the grains added in the upper 

 cup. 



Suppose, for example, that, on immersing the instrument 

 in ether, it requires 34 grains in the top cup to make it 

 subside to the middle mark on the stem. The specific gra- 

 vity of such ether will in this case be 700 -f 34 = '734. 

 And on putting the instrument into alcohol or wort, if it 

 requires in the former case 125 grains, and in the latter 355, 

 the specific gravity of the spirit will be -825, and that of 

 the wort ]'055. 



To ascertain the specific gravity of a solid, ve have to take 

 any fragment less than 300 'grains ; find its ivciglit in airy 

 and its weiglit in water , and take their difference ; and on 



dividing 



