54° On the Analysis of 
smalla portion of the earthy salt. The other 
earthy salts, or those of magnesia, barytes 
and alumine produce the same effect nearly, 
but they are rarely met with, compared with 
those of lime. 
When any earthy salt is dissolved in pure 
distilled or rain water, it increases the spe- 
cific gravity of the water; but in the instance 
of spring water in general this test is rendered 
of little use, because the increase of sp. gr. 
is so small as almost to elude the nicest in- 
strument that can be made. I have however 
an instrument, made by an artist in this town, 
which is nothing more than the common glass 
hydrometer, but with an unusually fine small 
stem, that shews the superior gravity of 
spring water. It cannot indeed be brought 
in competition with other methods for ascer- 
taining the relative hardness of spring water, 
but it is a most useful instrument in other de- 
partments of chemical investigation, particu- 
larly in determining minute portions of resi- 
dual salt after precipitations.* It may well 
* The scale of the hydrometer is 14 inch long and it is 
divided into 25°, each degree corresponding nearly to 
.0004 ; the difference between distilled water and common 
spring water is usually about 1° on the instrument; and 
that between distilled or rain water and the strongest 
lime water is 4°. 
