84 ADVANTAGE OF ACQUAINTANCE WITH CHEMICAL COMPOUNDS. 
will each combine with the same quantity of 
any other substance, as 10 of sulphur. This 
law was inferred by Richter from a fact first 
observed by himself ; viz. that when two neu- 
tral salts decompose each other, the resulting 
salts are likewise neutral. Thus, sulphate of 
soda being added to muriate of lime will give 
perfectly neutral sulphate of lime and muriate 
of soda. The reason of this will immediately 
appear, on considering the equivalents of these 
substances ; thus, if we take 72 parts of sul- 
phate of soda and 05 parts of muriate of lime, 
the following decompositions take place : 
ts ( Soda. Muriatic Acid. g 
■2 32 37 I S 
cS i I rl 
^ 1 “ P 
St 1 Sulphuric Acid. Lime. §’ 
w L ^0 28 J o 
Here the 40 parts of sulphuric acid combine 
with the 28 parts of lime, and the 37 of muri- 
atic acid with the 32 of soda, no part either 
of the acid or alkali remaining in an uncom- 
bined state. The neutrality will not be at all 
affected by our taking more or less than 72 
parts of sulphate of soda; for if we take 
more, some of the sulphate of soda will remain 
undecomposed ; if less, we shall have some 
of the muriate of lime remaining. From this 
observation Richter inferred, that^ the quan- 
tities of ttvo alkaline bases, sufficient to neu- 
tralize equal weights of any one acid are pro- 
portional to the quantities of the same bases 
requisite to neutralize the same weights of 
every other acid. For instance, (i parts of 
potass and 4 of soda neutralize 5 of suUhuric 
acid ; and 4.4 of polass are sufficient to 
saturate 5 of nitric acid. Therefore, to find 
the quantity of soda sufficient to saturate this 
weight of nitric acid, we institute the follow- 
ing proportion : as ihe potass equivalent to 
the sulphuric acid is to the potass equivalent 
to the nitric acid, so is the soda equivalent 
to the first, to the soda equivalent to the 
second ; or in numbers thus : as 6 : 44 ; ; 4 : 
2,93= the required quantity of soda. In a 
similar manner, if 80 parts of soda and 72 of 
lime saturate 100 parts of sulphuric acid, and 
if 109 parts of soda saturate 103 parts of muri- 
atic acid, \ve can then determine the quantity 
of lime sufficient to neutralize the 100 parts of 
muriatic acid ; thus 80 : 72 ; : 109 : 98= the 
required quantity of lime. 
The converse of this inference of Richter’s 
is also true ; viz. that the quantity of any two 
acids requisite to neutralize equal weights 
of any one base are proportional to the quan- 
tities of the same acids requisite to neutra- 
lize equal weights of any other base ; thus, 
126 parts of sulphuric acid and 87 of muriatic 
acid neutralize lOO parts of the soda, and 138 
of sulphuric acid neutralize 100 parts of 
lime, how much muriatic acid will produce 
the same effect ? This may be determined 
by the following proportion; as 126:87; : 
138: 95,3 = required quantity of muriatic 
acid. 
The advantage to be derived from an ac- 
quaintance with these principles of chemical 
combination in proportional quantitites, are too 
manifest from the examples already given to 
require further comment. By their aid cal- 
culations which otherwise would be tedious 
and difficult, may be made with ease and cer- 
tainty ; and the precise quantities of sub- 
stances necessary to produce any required 
effect at once determined, a matter of consi- 
derable importance to the success of chemi- 
cal manifulations in general, as well as to the 
conducting of pharmaceutical operations with, 
certainty and despatch. A few instances 
may be adduced from the Pharmacopoeia by 
way of illustration. 
If we want to test the strength of distilled 
vinegar, we have an easy and sure mode of 
doing it by ascertaining its neutralizing power. 
We know that the equivalents of acetic 
acid and of carbonate of lime coincide ; there- 
fore it is obvious that the quantity of marble 
dissolved by lOO grains of vinegar or any 
other solution of acetic acid will represent the 
percentage; of real acid in such a sample. 
For example, let 500 grains of such a solution 
of acetic acid be put into a basin or flask with 
10.) grains of marble in fragments, and after 
the first effervescence is over, warmed, and 
the neutrality ascertained ; the solution is then 
to be poured off and the remaining pieces of 
marble washed, dried, and weighed ; if 60 
grains have disappeared, 60 grains of dry 
acetic acid were present in the ouO grains of 
the solution employed. Again, sui)pose we 
wish to test the strength of any solution of 
hydrocyanic acid, we proceed as follows: to 
loo grains, or any other convenient quantity 
of the acid, contained in a phial, small quan- 
tities of the peroxide of mercury in fine pow- 
der are successively added, till it ceases to be 
dissolved. The weight of the oxide, divided, by 
4, gives the quantity of real acid present. The 
rationale of this test is ; the equivalent of the 
periode of mercury (216) happens to be just 
eight times that of hydrocyanic acid (27). 
Now, as the prussiate of mercury consists of 
two proportionals of acid to one of base, it is 
manifest that the quantities of acid and of 
base in the salt are in the ratio of 1 to 4. 
Again in the preparation of carbonate of mag- 
nesia, for example, the ingredients pi-escribed 
are sulphate of magnesia and carbonate of 
potass ; and the quantity of sulphate of mag- 
nesia directed being 23 parts, we may ascer- 
tain a priori the necessary proportion of the 
carbonate of potass, having recourse to their 
respective equivalents ; thus the equivalent of 
sulphate of magnesia is 123, and that of car- 
bonate of potass is 70. Now, 123 : 70 : : 25 ; 
14 q. p the proportion of carbonate of potass 
required. For other instances of useful ap- 
plication of the doctrine of equivalents to 
pharmaceutical purposes, see my Translation 
of the New Dublin Pharmacopoeia, where I 
have pointed out in the notes the advantage of 
this doctrine in determining a priori the re- 
quisite proportion of the several ingredients. 
The method of determining the proportonal 
numbers will be considered, when we have 
come to the subject of the Atomic Theory. 
