PROFESSOR GRAHAM ON OSMOTIC FORCE. 
183 
For 0’25 per cent 70 ms. (highest) 
1 per cent 63 ms. 
2 per cent 56 ms. 
Of salts having alkaline properties, phosphate of soda gave 705 ; borax, carbonate 
of soda and bicarbonate of soda all gave numbers which ranged above 60 ms. in 
various osmometers. 
To the same class also belong certain strong acids, phosphoric acid giving an 
osmose of 62 ms., glacial phosphoric acid of 73 ms. 
The caustic alkalies have probably too strong a disorganizing action upon the 
septum to allow osmose to proceed undisturbed. They give a positive osmose when 
present in a minute proportion, but very soon attain their terme moyen, and then 
become slightly negative. 
Caustic soda, 0*01 per cent., gave 24 ms.; 0 - 02 per cent., 29 ms.; 0*05 per cent., 
31 ms., which was the highest osmose observed ; (PI per cent., 22 ms. ; 0'25 per cent., 
3 ms. ; 1 per cent, and 2 per cent, of caustic soda gave both —10 ms. 
It appears most clearly that highly osmotic substances are also chemically active 
substances. Both acids and alkaline substances possess the affinities which would 
enable them to act upon the silicates of lime and alumina, which form the basis of 
the earthenware septum. Lime and alumina were accordingly found in solution after 
osmose, and the corrosion of the septum appeared to be a necessary condition of the 
flow. 
It was found impossible to exhaust the whole soluble matter of the walls of the 
earthenware osmometer, by washing, either with water, or with a dilute acid, for the 
process of decomposition appeared to be interminable. After such washings the 
action of an osmometer was often greatly modified upon salts of moderate osmose, 
such as chloride of sodium ; and similar changes gradually took place in the osmo- 
meters when used in ordinary experiments with saline solutions. 
It is on this account that I avoid the lengthened detail of numerous experiments 
which were made with the earthenware osmometer, and confine myself to general 
statements. 
Further, the potash salts were also largely kept back or absorbed by the earthen- 
ware, a phenomenon of the same class as the retention of alkalies by aluminous soils, 
which has been studied by Messrs. Thomson and Way. 
Other septa, which were not acted upon by the salts, were found deficient in 
osmotic activity, although possessed of the requisite degree of porosity. Gypsum, 
compressed charcoal, and tanned sole-leather, gave rise to no osmose when permeated 
by saline solutions. White plastic clay had an osmotic power which was quite in- 
significant when compared with that of baked clay : now the former may be con- 
sidered as an aluminous compound, upon which the decomposing action of water has 
been already exhausted, while the latter is in a form more liable to decomposition, in 
consequence of an effect of heat upon the constitution of the aluminous silicates of the 
