CAUSES OF THE MOTION OF JUICES. 353 
and have, when dissolved in water or other liquid, a very 
low capacity for diffusive motion. These bodies are 
termed Colloids,* and are characterized by swelling up or 
uniting with water to bulky masses (hydrates) of gelati- 
nous consistence, by inability to crystallize, and by feeble 
and poorly-defined chemical affinities. Starch, dextrin, 
the gums, the uncrystallized albuminoids, pectin and pectic 
acid, gelatin (glue), tannin and gelatinous silica, are col- 
loids. Opposed to these, in the properties just specified, 
are those bodies which crystallize, such as saccharose, glu- 
cose, oxalic, citric, and tartaric acids, and the ordinary 
salts. 
Other bodies which have never been seen to crystallize 
have the same high diffusive rate; hence the class is term- 
ed by Graham Crystalloids.t 
Colloidal bodies, when insoluble, are capable of imbib- 
ing liquids, and admit of liquid diffusion through their 
molecular interspaces. Insoluble crystalloids are, on the 
other hand, impenetrable to liquids in this: sense. The 
colloids swell up more or less, often to a great bulk, from 
absorbing a liquid: the-volume of a crystalloid remains 
unchanged. : 
In his study of the rates of diffusion of various sub- 
stances, dissolved in water to the extent of one per cent 
of the liquid, Graham found the following 
APPROXIMATE TIMES OF EQUAL DIFFUSION. 
Chlorhydric acid, erystalloid, 1. 
Chloride of sodium, ee 24. 
Sugar (cane,) % 
: Sulphate of magnesia, s 7, 
Albumen, colloid, 49. 
Caramel, fe 98. 
* From two Greek words which signify glue-like. 
+ We have already employed the word Crystalloid to distinguish the amor- 
phous albuminoids from their modifications or combinations which present the 
aspect of crystals, (p. 107.) This use of the word was proposed by Nigeli in 
1862. Graham had employed it,as opposed to colloid,in 1861. It will perhaps 
be found that Nageli’s crystalloids are crystalloid in Graham’s sense, 
