102 
ORIGINAL COMMUNICATIONS. 
when expressed in full, is to be enclosed in parentheses, and 
then connected to its fellow by the sign 4-. If more than one 
equivalent of either is concerned, the formula for multiple 
equivalents, constructed as before noticed, is to be connected 
by the sign -f with the formula of the single equivalent, 
which latter is enclosed in parentheses; as, for example, proto- 
sulphate of mercury, consisting of one equivalent of sulphuric 
acid and one of protoxide of mercury, is denoted by (Hg + O) 
+ (S 4- 30), and the bisulphate of the peroxide, composed of two 
equivalents of sulphuric acid, and one of peroxide of mercury, 
by (Hg+20) + 2(S + 30.) The sign + between the elements 
of the primary compound, may be omitted, and the multipli- 
cation indicated by the small figure to the right. The 
notation being thus modified, the parentheses become un- 
necessary, and the same compounds will then be expressed 
by HgO + SO 3 , and Hg0 2 +2S0 3 . Finally, if the dots be 
used, a still more concise expression is obtained, and these 
compounds will be denoted by Hg + S and Hg + 2S. 
The formulae for the more complicated compounds are 
formed upon the same principles, as will be apparent on 
examining those of any of the double salts. Thus the fol- 
lowing formula expresses alum, a compound of one equivalent 
of sulphate of potassa and one of tersulphate of alumina, 
(KO + SO 3 ) + A1 2 3 ( + 3S0 3 .) 
In many cases the sign +, as used in the above formula, is 
dispensed with, and its place supplied by a full point or comma. 
The formulas are thus brought into a smaller compass without 
any further alteration, the effect of these points and the sign 
being precisely the same. They cannot, however, be used 
in all cases as substitutes for the -j-j except in the elementary 
formulas. In the more complicated examples, their use is 
allowable in some part but not in others. This is to be re- 
gulated by the mode in which the compounds are united, 
taking care that the distinction between the several compounds 
may be clearly pointed out by the use of these signs. Thus, 
instead of stating the composition of alum as above, this sub- 
