ON THE SPECIFIC GRAVITY OF SULPHURIC ACID, 7 
If tberefore one equivalent SO, cannot chemically combino with more than 
six equivalents of water, and to a certain quantity of acid more water w poured 
than is necessary to form tliis hydrate, so at length every equivalent of bO, 
will unite itself with six equivalents of water, and the flmd must conBcquontly 
be considered as a simple mixture of that hydrate (SO, + 6H,0) with the 
remaining water. In this case there is reason to expect that the specific 
gravity of the mixture will be equal to die mean specific gravity of both its 
constituent parts. But that this is not the case is easily proved. If, m a 
mixture of two different fluids, p' and y'denote the quantity according to 
weight which one portion of the mixture contains of both constituent parta, 
s' and s" the specifle gravity of these, and S the mtan speci6c gravity of the 
mixture, then the volumes of the two mixed substances will be = 
and consequently the mean specific gravity of the mixture 
w — TTi- y,'' + y'”’ 
x-P- 
s' s" 
or because p' + p" = 1> p'' = 1 —p'> so is 
s= ■’* 
t' —p' (s' — 
Now if p' signifies the quantity SO, + flHgO which n acid con- 
ins, s' the specific gravity of this hydrate = 1*40998, and s the specific 
tains, 
gravity of water = 1, then 
S = 
1*40998 
1 
1-40998 — 0*40998p' 1 — 0*29077p'' 
or whenp, as before, signifies the quantity of dry acid void of \vaU'r which 
one part of the mixture contains, then p' = 0*42615p> and consequently 
S =- \ - = 1 + 0*68233p -f &o. 
1-0158233P 
If this expression is compared with the value of the constants in Uie equa¬ 
tions (A.), it will easily be seen that this mean specific gravity w always 
smaller than the truth us found by the experiment. The difference 
both, for such degrees of dilution tliat the square of p need not be corwidcrrt, 
is equal to 0*1575Sp, or, for instance, for p = 0*1 . nineteen tomes grea r 
than the probablo error of observation. A very diluted sulphurtc acid i* 
consequently no simple mixture of SO, + 6lt,0 with w’atcr; but^h ct»n- 
slitueiit paru have such an etfeeton each other, that the volumo of me mi - 
tore is constantly less than the sum of the volumes of the niixecl floitU a e 
same leniperature. . .. . 
This result made me at first believe that perhaps there ® .’f’ . 
hydrate than SO, + 6HoO, and that therefore the fluiil might be 
mixture of that hydrate with more water. 1 calculated therefore , 
twenty observations fromp =0*00815 top=0*1631 according to the o 
S 5=. . ... 
1 — xp 
and found the most probable value of the constant a? to be 
X = 0*7630667 + 0*0020280, 
(*.) 
