CHEMISTKY. 



215 



line and diffusible, which he names crystal- 

 loids; 2, the amorphous and non-diffusing, 

 which he names colloids (*oXXa, glue). Any 

 substance separated by diffusion is named a 

 diffusate. For an application of the process 

 in case of silica, see BUILDING MATERIALS. 

 The most diffusive of known substances are 

 hydrochloric acid and the allied hydracids ; and 

 next in the scale are the solid chlorides, but 

 particularly those of potassium and sodium. 

 The times required for an equal diffusion of the 

 following substances, were hydrochloric acid, 

 1 ; chloride of sodium, 2.33 ; sugar, and sul- 

 phate of magnesia, 7 ; albumen, 49 ; caramel, 

 98. The rates of diffusion are accelerated by 

 heat; and they are less in alcohol and other 

 liquids than in water. 



Generally, the new process serves for sepa- 

 rating a crystalloid from associated colloids, or 

 the reverse, and to some extent for separating 

 the more from the less diffusible bodies. 

 Among particular applications, are those of 

 purifying certain colloids albumen dissolved 

 in water with acetic acid being in this way 

 after 3 or 4 days entirely freed from the alka- 

 line and earthy salts, and with retention of 

 the sulphur which enters into its constitution. 

 In like manner, arsenious acid and certain other 

 poisons are separable from organic substances, 

 and in great purity, so that the method must 

 prove valuable in cases of suspected poisoning. 



Liebig has claimed that Graham's explanation 

 of diffusion to the effect, namely, that crys- 

 talloids are bodies which by their affinity for 

 water can abstract it, molecule by molecule, 

 from gelatinous masses or moist septa, and can 

 BO advance gradually through the latter, while 

 colloid bodies by their want of affinity for 

 water have no such power is identical with 

 that proposed by himself in relation to motion 

 of liquids in the animal body, in 1848. He 

 calls attention also to the importance of dialy- 

 sis in the study of the chemical constitution 

 of the animal and vegetable secretions. 



The colloids are the inert bodies, but having 

 great sensibility to external conditions, and 

 being thus highly mutable or unstable. The 

 crystalloids are chemically active or energetic, 

 but unsusceptible to external agencies. But 

 the mutability of the former fits them for the 

 part which some of them have to play in the 

 metamorphoses of living tissues, in connection 

 with nutrition, decomposition, and the mani- 

 festation of vital force ; while the more unal- 

 terable crystalloids have no such capacity. 

 Thus, these elements stand physiologically in 

 relations the reverse of those they show chem- 

 ically ; and Graham accordingly terms the 

 crystalloid a statical, and the colloid a dynam- 

 ical condition of matter. 



At least two economical applications of dial- 

 ysis have been very recently proposed. Dr. 

 Marcet has dialyzed in small quantity the brine 

 or refuse liquor from the curing of meat, and 

 having by the process separated the salt, the 

 liquor containing the juices from the meat be- 



comes fit for use as an article of diet. He sug- 

 gests that if this separation can be effected 

 without too great cost on the large scale, the 

 liquor could be converted into soup for prisons 

 and penitentiaries, or, in the present crisis, for 

 the half starved cotton-spinners of Lancashire. 

 It has also been suggested that the much de- 

 bated question of utilization of town sewage 

 may perhaps be solved by the process of dial- 

 ysis. The solid matters of the sewage are 

 diffused through so enormous a quantity of 

 water as to render the whole comparatively 

 valueless. But these solid matters consist of 

 crystalloids (salts of various character) and col- 

 loids (organic substances) ; and the former are 

 the materials, the return of which to the soil is 

 especially to be desired. The question now 

 raised is, whether dialysis can be economically 

 applied to the separation in compact form and 

 saving of these mineral elements of fertility of 

 soils. 



VII. TRANSPIRATION (Liquid), in its relations 

 to chemical composition. The phenomena of 

 passage of liquids under pressure through 

 capillary tubes, first developed by M. Pois- 

 seuille, Prof. Graham has recently studied, under 

 the name of Liquid Transpiration. To this study 

 he was led by remarking that alcohol diluted to 

 different degrees, is most retarded in its pas- 

 sage through a capillary tube at that degree at 

 which the greatest condensation of the mixed 

 liquids takes place. This he understood to 

 indicate that the definite hydrate of alcohol 

 containing 6 equivalents of water was the one 

 most retarded; and if so, the rat8 of trans- 

 piration appears to depend on chemical com- 

 position, and to indicate it. This new physi- 

 cal property might thus become available, like 

 the boiling point and others, as an aid in fixing 

 chemical composition. The trials made on 

 other alcohols and hydrated acids appear to 

 establish a relation between transpirability and 

 composition. Of nitric acid (NO 5 , HO) with 

 water added in successive proportions up to 

 100 parts, the maximum time of transpiration, 

 at 20C., was at the dilution corresponding to 

 3 equivalents of water; the time being then 

 2.1034 (taking that of water as 1), and dimin- 

 ishing both ways. In case of acetic acid, the 

 greatest time was at the dilution answering to 

 2 equivalents of water; in that of sulphuric 

 acid, it was also at 2 equivalents. Eelation of 

 transpiration time to boiling point is shown in 

 the alcohols, thus: 



Thus, generally, slow transpiration and low 

 volatility appear to go together, and to be 

 connected with a heavy molecule ; in this way, 

 it would appear, the water added to hydrated 

 alcohols and acids acts to impede their trans- 

 piration. A fixed temperature being desirable 



