224 ANNUAL OF SCIENTIFIC DISCOVERY. 



held at different temperatures. The acetate of potash appeared to 

 coincide in diffusibility with the same group, and so did the ferrocya- 

 nide of potassium. The nitrate of potash, chlorate of potash, nitrate 

 of ammonia, chloride of potassium, and chloride of ammonium, formed 

 another equi-diffusive group. The times in which an equal amount of 

 diffusion took place in these two groups appeared to be as 1 for the 

 second to 1,4142 for the first, or as 1 to the square root of 2. Now 

 in gases the times of equal diffusion are as the squares of the densities 

 of the gases. The relation between the sulphate of potash and nitrate 

 of potash groups would therefore be referred to the diffusion-molecule 

 of the first group having a density represented by 2, while that of the 

 second group is represented by 1 . The relation of the salts of potash 

 to those of soda, in times of equal diffusibility, appeared to be as the 

 square root of 2 to the square root of 3 ; which gives the relation in 

 density of their diffusion-molecules as 2 to 3. Hydrate of potash and 

 sulphate of magnesia were less fully examined, but the first presented 

 sensibly double the diffusibility of sulphate of potash, and four times 

 the diffusibility of sulphate of magnesia. If these times are all 

 squared, the following remarkable ratios are obtained for the densities 

 of the diffusion-molecules of these different salts, each of which is the 

 type of a class of salts: Hydrate of potash, 1 ; nitrate of potash, 

 2 ; sulphate of potash, 4 ; sulphate of magnesia, 16 ; with nitrate of 

 soda, 3 ; and sulphate of soda 6. It is these diffusion-molecules of the 

 salts whichtare concerned in solubility, and not the Daltonian atoms 

 or equivalents of chemical combinations ; and it is observed that a 

 knowledge of the diffusibility of different substances is required for 

 the study of endosmosis, in which the effect due to diffusibility should 

 be distinguished and separated from the proper action of the mem- 

 brane employed. Prof. Graham's Bakerian Lecture, Royal Society. 



ON THE CONDENSATION OF VOLUME IN HIGHLY HYDRATED 



MINERALS. 



DR. PLAYFAIR called the attention of the British Association to the 

 remarkable fact of the condensation of water in those bodies which 

 contain that fluid in combination with solid matter. If a salt contain- 

 ing water of crystallization be dissolved in a measured quantity of 

 water, it is found that its solid matter occupies really no space, the 

 water in which it is dissolved increasing in bulk only by the quantity 

 of water contained in it. In other words, it appears, that in many 

 solid bodies, which contain water in a state of chemical combination, 

 such a condensation occurs that they occupy no greater space than the 

 w r ater contained in them would if frozen into ice. Jameson's Jour- 

 nal, Oct. 



PHOSPHORUS IN COPPER, WITH A NOTICE OF EXPERIMENTS ON 

 THE CORROSIVE ACTION OF SEA-WATER ON COPPER. 



THE Civil Engineer and Architect's Journal, for November, 1849, 

 contains a paper by Dr. Percy on " phosphorus in copper." Upon 



