112 
POPULAR SCIENCE REVIEW. 
On a Means of Utilizing the Phenomena of Super saturation. — M. Jeanuel 
suggests that this phenomenon may he utilized in the purification of sul- 
phate of soda and other commercial salts. For sulphate of soda, proceed as 
follows: — Take 300 grammes of this salt and 100 grammes of distilled 
water ; dissolve at a temperature of 33° in a glass flask, and while this is 
going on, arrange a filter in a funnel and pour through it 500 grammes of 
warm water at about 50°. Then place the funnel on a wide-mouthed flask 
well rinsed with distilled water, pour the warm saline solution on the filter, 
and cover it with a plate of glass. The solution will entirely pass through 
without crystallizing, and will remain liquid in the flask even after cooling. 
When the funnel is removed, the solution, exposed to the air, rapidly 
crystallizes and becomes heated. When quite cold, decant the mother 
liquor. Sulphate of magnesia, sulphate of zinc, and carbonate of soda may 
be purified in a similar manner. The acetate and tartrate of soda, soluble 
in their water of crystallization at a temperature below 100°, may be easily 
filtered by this means. This process is not applicable to alum. M. Jeanuel 
proposes to use this phenomenon as a means of separating salts ; thus, dis- 
solve 335 grammes of nitre and 300 grammes of alum in 100 grammes of 
water j allow the mixture to cool without exposure to the air, and the nitre 
will crystallize out, whilst the alum will remain in a state of supersatura- 
tion. The separation of the two salts can thus be effected by decantation. 
The Earth and Moon in Collision. — Mr. James Croll, who some time since 
asserted that owing to peculiar solar and lunar action the above extraordinary 
condition will eventually take place, has just published a paper reasserting 
the truth of his proposition. The theory was opposed by the Astronomer 
Royal and Professor William Thomson, who showed that, owing to the 
position of the tidal wave, the moon is drawn not exactly in the direction 
of the earth’s centre of gravity, but a little to the east of that centre, and 
that in consequence of this she is made to recede from the earth. Her 
orbit is enlarged, and her angular motion diminished. This argument 
does not, in Mr. Croll’s opinion, affect his view. The conditions described 
by Professor Thomson and the Astronomer Royal do not in the least 
degree prevent the consumption of the vis viva of the earth’s motion round 
the common centre of gravity, although to a certain extent, at least, it must 
prevent this consumption from diminishing the moon’s distance, and in- 
creasing her angular motion. But as this consumption of vis viva will go 
on through indefinite ages, if the present order of things remains unchanged, 
the earth and the moon must therefore ultimately come together. 
The Dynamical Theory of Electricity. — Mr. Charles Brooke has addressed 
a letter to the Editor of the Philosophical Magazine, alleging that he sees 
more reason than ever for believing in the dynamical theory. He gives the 
following fact, as strongly confirmatory of the dynamical doctrine. It has 
long been known that if a bar of antimony and one of bismuth be con- 
nected, and a current be transmitted from antimony to bismuth, heat will 
be developed at the point of junction ; and, on the contrary, if the current 
pass from bismuth to antimony, cold will be produced. Now it has occurred 
to Mr. Brooke, that if in the former, as in all cases where heat is developed 
in the passage of a current u a portion of electric potential is converted into 
thermic potential, or heat,” there ought in the latter case to be an inductive 
