PROFESSOR GRAHAM ON OSMOTIC FORCE. 
213 
the weighings arose from the presence of organic matter dissolved out of the mem- 
brane, of which it gives the quantity probably somewhat exaggerated. 
First diffusate, 0'328 grm. sulphate of potash. 
Second diffusate, 0 362 grm. sulphate of potash, 0-019 grm. organic matter. 
Third diffusate, 0-351 grm. sulphate of potash, 0"031 grm. organic matter. 
Fourth diffusate, 0-366 grm. sulphate of potash, 0-025 grm. organic matter. 
Fifth diffusate, 0'356 grm. sulphate of soda, 0-011 grm. organic matter. 
Sixth diffusate, 0"339 grm. sulphate of soda, 0'019 grm. organic matter. 
Seventh diffusate, 0-334 grm. sulphate of soda, 0‘009 grm. organic matter. 
Eighth diffusate, 0’239 grm. sulphate of zinc. 
Ninth diffusate, 0-260 grm. sulphate of zinc. 
The diffusates of the two alkaline sulphates are remarkably uniform, the diffusate 
of sulphate of soda falling a little under that of sulphate of potash, but not so much 
as in open vessels. The diffusate of sulphate of zinc is still smaller but relatively 
too high, as it should not much exceed one-half of that of sulphate of potash, 
judging from the diffusion of these salts in the absence of membrane. The organic 
matter accompanying the salt falls off in quantity in successive experiments, but 
continued to exist to the last, although it was not determined in the experiments 
with sulphate of zinc. The diameter of the disc of membrane was 123 millimeters, 
and its original weight, air-dried, 0"559 gramme. 
Oxalate of Potash , Chromate and Bichromate of Potash . — The only property of 
sulphate of potash which seems to be connected with the positive osmose of that salt, 
is its bibasicity as a sulphate. The alkaline character promotes positive osmose, 
and this character appears to be a distinction of polybasic salts. The common 
tribasic phosphate of soda is strongly alkaline to test-paper, and the bibasic pyro- 
phosphate of soda enjoys the same property in a still higher degree. The sulphates 
of potash and soda are certainly neutral to test-paper, but they may be looked upon 
as potentially alkaline from the easy severation of the second equivalent of fixed base 
and its replacement by water, witnessed in all bibasic salts. In monobasic salts, 
on the contrary, a proclivity to the acid character may be suspected. Thus although 
the chloride of potassium and nitrate of potash appear as neutral to test-paper as 
the sulphate of potash is, yet the chlorides and nitrates of the magnesian bases are 
more decidedly acid than their sulphates. It is just possible then on this view, that 
the osmotic inferiority of chloride of sodium, and the power of that salt to counteract 
the positive osmose of carbonate of potash, may be exhibitions of acid character 
belonging to the former salt. The observations of the rise in the osmometer of 
chloride of sodium, and also of the chlorides of barium and calcium, previously 
described, also have the appearance of being the effect of diffusion, modified by a 
slight chemical osmose of a negative character proper to these salts. 
The polybasic constitution of oxalate of potash is well marked, and its positive 
