4 
beaume's hydrometers. 
ble to supplant it with one giving different though more correct 
values ; the only thing that can be done is to remove trie cause of 
its errors, and to place it upon a true and scientific basis, by which 
correct tables may be formed for the value of its degrees, and 
which, by being recognised as a standard by competent authority, 
will enable the maker to give it; a degree of accuracy now unob- 
tainable. 
Beaume's hydrometer, whether made in England, France, Ger- 
many, or this country, have always the 66° equal in strength to 
commercial sulphuric acid. Nearly all of them are marked with 
an arrow or other device to show that that is considered the level 
to which it should sink in the acid ; as the maker has no authority 
by which to decide the proper strength of the acid, it compels him 
to take for granted that it is of uniform strength, which by no 
means is the case. Most systematic chemical works unite in 
stating that it is about 1.843 or 1.845, a degree of concentration 
rarely met with. The mean of several trials of samples, obtained 
from full carboys made by three different houses in this city, give 
a result of 1.8366. 
The table published in Wood & Bache's Dispensatory, and 
which is nearer correct than any other I have met with, gives 
66° = 1.8312, taking 1.8354 as 'the standard sp. gr. for 66° (the 
advantage of which is that it gives a number without fractions for 
a modulus,) we have the formula for the hydrometer, giving 
1.0740 as the sp. gr. for 10°. As 1.0740 differs from 1.0735 (the 
density given by Beaume's 10 per cent, solution,) only by 
it is evident the manner in which the present scale has come into 
use. The makers noticing that 10 per cent, salt gave 10°, and 15 
per cent. 15°, erroneously thought that ]0° of one scale was equal 
to the 10° of the other, and to save the trouble of preparing two 
solutions, substituted the 10 per cent, for the 15 per cent. This 
probably was the case before the density of commercial acid was 
established at its present strength, and, therefore, would not attract 
attention by the error. 
If, then, 1.0740 is recognised as the standard sp. gr. for 10° B., 
1.8354 will be the sp. gr. corresponding to 66°, and if the instru- 
ment maker takes proper care in ascertaining that his acid is of 
