538 Proceedings of the Royal Society 
appear to me very interesting, and to open up a line of research 
likely to lead to important results as to the laws of solution and 
chemical affinity. The following are the more important facts as 
yet determined : — 
1. NaCl and HCl . — To a saturated solution of common salt 
(HaCI) was added some strong hydrochloric acid (HCl). Salt was 
rapidly precipitated on each addition of acid. This action of HCl 
is usually described by saying that salt is insoluble in hydrochloric 
acid, but the mode of action does not seem to have attracted atten- 
tion. The following experiments throw some light on the matter. 
2. Na 2 SO± + I0H 2 0 and HCl . — To a saturated solution in 
water of sodium sulphate was added strong solution of hydrochloric 
acid. Anhydrous sodium sulphate was quickly precipitated. This 
precipitate was quickly dissolved on the addition of a further 
quantity of HCl. In this case it cannot be said that anhydrous 
sodium sulphate is insoluble in hydrochloric acid, because it is 
dissolved by it when added after its precipitation. The action is 
exactly analogous to what occurs when ammonia is added to a salt 
of zinc ; the ammonia first combines with the acid of the zinc salt 
throwing down a precipitate of zinc oxide, then, on a further 
quantity of ammonia being added, the zinc oxide is dissolved. In 
like manner, in the case of solution of sodium sulphate the HCl 
first combines with the water and precipitates the anhydrous salt, 
and then, by a further addition of acid, the salt is again dissolved. 
This is made more clear by the next experiment. 
3. Crystals of Na 2 SO± + 10 H 2 0 and HCl . — Strong hydro- 
chloric acid was poured over some undissolved crystals of sodium 
sulphate. Rapidly the crystals were broken up, the water uniting 
with the acid, and the anhydrous salt left, which, as in the former 
case, was dissolved by the addition of more acid. 
4. CaCl 2 and HCl . — To a saturated solution in water of calcium 
chloride was added some strong hydrochloric acid. Ho action was 
apparent. As calcium chloride has a strong affinity for water, I 
concluded that the affinities were balanced in the two solutions, and 
therefore there was no action. To upset this balance, if it existed, 
I added to the hydrochloric acid solution some fragments of solid 
calcium chloride, which, as anticipated, rapidly dissolved with 
effervescence, expelling hydrochloric acid gas copiously. Further, 
