1877 *] Notices of Books. 277 
the gas in question of uniform density throughout. Mr. Graham 
carefully points out that the phenomena of diffusion and effusion 
are essentially different, although the rates of passage are alike ; 
diffusion only permits molecules to pass, but masses pass by 
effusion. 
He found that if the orifice in the platinum disc became 
tubular, the passage of carbonic acid and nitrous acid became 
quicker in relation to air than when the rates of passage through 
a thin pundtured disc were examined, and from fadfs such as 
this a new kind of passage was detected, which he called trans- 
piration. By employing capillary tubes the effusion and trans- 
piration rates of passage were found to differ widely, “for if the 
length of the tube is progressively increased, and the passage of 
all gases becomes greatly slower, the velocities of passage of the 
different gases are found to diverge greatly from their effusion 
rates.” The velocities at last, however, attain a particular ratio 
with a given length of tube and resistance, and preserve the same 
relation to each other with greater lengths of tube and resist- 
ances ; the most simple result being probably that of hydrogen, 
which has exadlly double the transpiration rate of nitrogen, the 
relation of these gases as to density being as 1 : 14. Mr. 
Graham viewed transpirability as being a kind of elasticity, 
depending upon the absolute quantity of heat which different 
gases contain under the same volume, and it is therefore more 
immediately connected with specific heat than with any other 
property of gases. One very important branch of Mr. Graham’s 
labours appear to have commenced in 1829, with a notice of the 
“ Singular Inflation of a Bladder,” which was two-thirds filled 
with coal-gas, and on being introduced into carbonic acid for 
some hours became distended. Mr. Graham pointed out that, 
although Dutrochet would probably view in the experiment the 
discovery of endosmose adting upon aeriform matter as he had 
observed it to adt upon bodies in a liquid state, the penetration 
of the carbonic acid was really preceded by an adtual absorption 
in the water with which the pores of the bladder were filled. He 
continued the research at intervals and published a series of 
papers a few years before his death, in which he showed that the 
penetration of gases through colloid septa, such as india-rubber, 
was the result of an adfual occlusion or absorption. A com- 
parison of the relative rates of the penetration of oxygen and 
nitrogen through india-rubberledtoamost remarkable experiment. 
Oxygen penetrates 2 £ times as fast as nitrogen ; therefore by 
dialysing air Mr. Graham actually increased the quantity of 
oxygen from 20-8 to 41 per cent, just as he had effedted a partial 
separation of oxygen from air by the slightly greater diffusion 
velocity of nitrogen. The phenomena of diffusion and penetra- 
tion of india-rubber are, however, widely different, for the rate of 
passage through the colloid depends on the facility with which 
the gas is capable of being liquefied within its pores. MM. 
