1866. | Chemistry. 265 
durability. A mixture of the same magnesia with chalk or powdered 
marble made into a plastic mass, and placed in water, soon becomes 
extremely hard ; and M. Deville hopes in this way to get a modelled 
bust converted into artificial marble. 
Dolomite calcined at a low red heat and powdered, and then 
made into a paste, forms under water a stone of extraordinary 
hardness. 
It has long been known that calcined magnesian limestone forms 
a very strong hydraulic cement; and Dr. C. Calvert has shown that 
the strength of the cement is in direct proportion to the amount of 
magnesia. Dr. Calvert also confirms the statement of M. Deville, 
that the calcination of magnesian stones must be carefully managed, 
too high a temperature completely destroying the hydraulicity of 
the material. It seems important also that the calcined product 
should be very finely ground to improve the setting. 
Harrogate water has long enjoyed some celebrity as a remedial 
agent, but the recent analysis of one spring by Dr. Sheridan Muspratt* 
is likely to bring it into still greater repute. The eminent chemist 
above named has discovered in what is known as the “ Cheltenham 
spring,” a large proportion of protochloride of tron, as much indeed 
as 16°011 grains in the imperial gallon. This, therefore, is the 
strongest chalybeate spring known, and as the condition in which 
the iron exists is one of the most favourable for its assimilation by 
the animal economy, the water is likely to prove most efficacious in 
all those affections, too numerous to mention, for which iron is pre- 
scribed. It deserves mention that chloride of barium is also present 
in the water in unusually large quantity, but this will not detract 
from the medicinal value of the spring. 
Passing to the mention of other mineral elements, we find an 
easy method of accomplishing what has hitherto been found a diffi- 
cult object. It is a process by M. Terreil, for separating cobalt and 
nickel in minute quantities. Toa solution containing the two metals 
together with manganese, the author adds ammonia, until the pre- 
cipitate first formed is redissolved. He then makes the solution 
hot, and adds a solution of permanganate of potassium until the 
mixture acquires a permanent violet colour. After this the solution 
is boiled for a few minutes with a slight excess of hydrochloric acid, 
and after having been kept hot for some time, it is set aside for 
twenty-four hours. At the end of this time the cobalt is deposited 
as roseo-cobaltic hydrochlorate, 100 parts of which contain 22°71 of 
cobalt. To separate the nickel in the residual liquor, the manganese 
is precipitated by first saturating the liquor with ammonia, and 
then adding an alkaline hypochlorite. This throws down all the 
manganese, and the nickel remains in the solution, from which it 
* «Chemical News,’ vol. xiii., p. 26. 
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