32 Proceedings of the Royal Physical Society. 
out into a flask, and the solution of common salt poured 
on to it. The whole was digested for four days at a 
constant temperature of 18°35 C., with occasional stirring. 
The solution was then filtered through a dry filter, and 
100 ec.c. taken at 15°5 C. for estimation of the lime in 
solution. The determination was effected in the usual way 
by precipitation with ammonium oxalate, and the pre- 
cipitate, after drying, was ignited in a platinum crucible 
over the blow-pipe till it ceased to lose weight, and was 
weighed as pure lime, CaO. The weight of lime so obtained 
was calculated back to calcium sulphate, SO,Ca.2OHg2. 
The following table summarises the results obtained, which 
have been confirmed by duplicate experiments. I also 
append a curve, which shows more clearly than the figures 
the progressive increase in the solubility of gypsum as the 
solution of common salt is strengthened :— 
Solubility of Gypsum (SO,Ca.20H2) in Solutions of Common 
Salt (NaCl). ' 
Strength of NaCl Grammes of S04Ca.20H2 
Solution. in 100 c.c. Solution. 
1 per cent. 4380 
MEISE 5403 
ears. 6244 
aeeae = 3 6960 
Sty yee ‘7464 
7s Bee ae, 8081 
yt eabet 8360 
pare 8711 
ee ae 8944 
nots okay ‘9079 
ELS; ~ Os 9310 
Pure water, "2616 
It will be observed that a solution of common salt of about 
the same strength as sea-water, 7.¢., 3 per cent., increases the 
solubility of gypsum nearly threefold, and that above 8 per 
cent. the increase in the solubility is only trifling. 
