SCIENTII'IC SUMMAEY. 
239 
Dialysis in. the Examination of the Constitution of Plants. — It lias lately- 
been stated that when the juices of plants are placed upon the dialyser the 
mineral elements are readily obtained. In the course of some experiments, 
made with a view of proving the accuracy of these assertions, the folio-wing 
results were obtained ; — The ’ tops of the common potato yielded crystals of 
nitrate of potash, some cubes of chloride of potassium, hexagonal crystals not 
analysed, sugar, and an ammonia salt. The “ deadly nightshade ” gave 
nitrate of potash, an unkno-wn magnesia salt in square prisms, and sugar. 
The common garden lettuce contained crystals of nitrate of potash, tetrahedra 
of undetermined composition, sugar, and ammonia. Cucumbers furnished 
sugar, ammonia, and sulphate of lime. Cabbage gave sulphate of lime and 
ammonia ; and the thorn-apple contained so much nitrate of potash, that 
dried portions quite deflagrated on being ignited. — Vide Chemical News, 
Oct. 22. 
Copper Salts sensitive to Light. — An important observation has been made 
at Berlin to the effect that certain salts of copper have the property of under- 
going rapid change under the influence of light. This property was recently 
pointed out by Herr Griine, in a paper which was read before the principal 
photographic society of Prussia. A copper surface, when cleaned with 
hydrochloric acid, rapidly tarnishes, even after being well washed in water, 
and it never acquires as much brilliancy as when cleansed with sulphuric 
acid. This fact, though kno-wn for some time, was not explained upon the 
view that chloride of copper is sensitive to light until Herr Griine took it into 
consideration. Having often repeated the experiment of exposing ordinary 
culinary utensils to the action of light, he thought one day of preparing a 
copper plate in a similar manner, covering it -with an engraving and exposing 
it to the direct rays of the sun. After a few minutes’ exposure the design 
appeared upon the copper as a negative, and remained upon the plate for an 
hour after it had been exposed to the influence of diffused light, but 
eventually faded. Kepeated experiments satisfled the operator that com- 
mercial hydrochloric acid is preferable to that which is chemically pure. 
From an extended series of inquiries, Herr Griine has been enabled to 
establish the following generalization : — If we mix a concentrated solution of 
sulphate of oxide of copper with a solution of bichloride of zinc, a milk-white 
precipitate of per-chloride of copper is formed which blackens on exposure to ' 
light. This precipitate, however, is sensitive only in its moist condition, and 
pictures obtained with it fade away when the substance dries. The only 
thing required now is a means of fixing the impression produced by light. — 
Vide Photographic Journal, Oct. 15. 
Spontaneous Decomposition of Gun-Cotton. — In one of the numbers of the 
Comptes Bendus for September we find a paper by M. de Luca upon this 
I subject. We merely call attention to it in order to show that Frenchmen 
I not unfrequently make English discoveries, and publish them as if they were 
I quite their o-wn. In the memoir we refer to, the -writer very clearly demon- 
I strates that gun-cotton is exceedingly sensitive to the operation of light, and 
when exposed to the sun’s rays undergoes decomposition mto several new 
substances, which, however, he did not succeed in identifying. In concluding 
I his paper M. de Luca observed, “ When exposed to light and air, gun-cotton 
I decomposes spontaneously, contracting in bulk without losing either form or 
