SCIENTIFIC SUMMARY. 
525 
them a sort of syrupy liquid. The salts of these acids form solutions 
in water of very great density ; a solution of neutral silico-tungstate of 
soda, for example, may be made so dense that it will allow glass and 
quartz to float upon its surface. Hence, as Mr. Crookes suggests, this 
solution may possibly form an excellent material for prisms. — Vide The 
Chemical News , No. 232, p. 238. 
How to prepare Sub-oxide of Copper. — The following process for 
the preparation of sub-oxide of copper is given by Herr Boettger : — 
Dissolve, in two parts of hot distilled water, one part of crystallised 
sulphate of copper, one and a half of tartrate of potass and soda, and 
two parts of cane-sugar. When the solution is complete and tartrate 
of copper formed, add one and a half part of caustic soda. By boiling 
the mixture, the sub-oxide of copper is gradually precipitated, losing its 
odour completely, as in saccharometric experiments. The product is of a 
beautiful red colour, and, after it is washed and dried, will keep without 
alteration. — Vide Chemical News, May 7th, and Jour, fur prakt. Chemie , 
xc. 163. 
The Composition of Rain-water. — M. Bobierre, who lately presented a 
memoir to the French Academy, concludes from his experiments on and 
examination of rain-water : — 
1st. That the composition of specimens collected in large towns is 
extremely variable. 
2nd. These variations refer more especially to the proportions of am- 
monia, nitric acid, and organic matters. 
3rd. The examination of specimens collected at different heights show T s 
that there is a relation between the composition of the w T ater and the alti- 
tude at which it is received from the atmosphere. 
4th. In rain-water collected at Nantes in 1863, at a height of 47 metres, 
the proportion of ammonia was 1*907 gramme per cubic metre, whilst 
that collected at a height of seven metres in a low and unhealthy neigh- 
bourhood contained 5*939 grammes per cubic metre of the same substance. 
5th. The proportion of nitric acid increases as that of ammonia 
diminishes. 
6th. The evaporation of 372*50 litres of Nantes rain-water proved that 
the variation of alkaline chlorides and organic matter is much more 
marked than that of other substances. — Vide Comptes Rendas, lviii. 17. 
Chemical Preservation of Statues. — This may be achieved by following the 
processes lately described at the French Academy. One of these methods 
is that of M. Dalemagne, who thinks that coating such objects with silica 
is quite sufficient to ensure their preservation. In proof of this he 
calls attention to the circumstance that certain busts which were sub- 
mitted to the process of silicatization ten years ago are now in a state of 
perfect preservation, whilst others of the same age placed under the ordi- 
nary conditions of the atmosphere, and even to which considerable atten- 
tion had been paid, are now in a state of more or less marked decay. 
A crystallized Hydrate of Soda. — Herr Harms has obtained a well- 
crystallized and definite hydrate of soda, by exposing a solution of caustic 
soda of density 1*385 to a temperature of 0° centigrade. The crystals are 
often very large, have a glassy lustre, and are perfectly transparent and 
YOL. HI. — NO. XII. 2 N 
