CAUSES OF THE MOTION OF JUICES. B02 
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 pectie 
acid, gelatin (glue), tannin and gelatinous silica, are col- 
loids. Opposed to these, in the properties just specified, 
are those bodies which erystallize, such as saccharose, g¢lu- 
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.+ 
Colloidal bodies, when *nsoluble, 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 lexs, often to a great bulk, from 
absorbing a liquid: the volume of a crystalloid remains 
unchanged. 
In his study of the rates ¢t diffusion of various sub- 
stances, dissolved in water to thé extent of one per cent 
of the liquid, Graham found th« wllowing 
APPROXIMATE TIMES O¥ QUAL DIFFUSION, 
Chlorhydric acid, nystalloid, 1. 
Chloride of sodium, “ 2h 
Sugar (cane,) BN 7 
Sulphate of magnesia, 0 7, 
Albumen, ~olloid, 49. 
Caramel, $ 98. 
* From two Greek words which signify glue-liye. 
t+ We have already employed the word Crystalied to distinens\ the amor 
phous albuminoids from their modifications or come rtinns whic esent the 
aspect of crystals, (p. 107.) This use of the word was prodosed Fy Fegeli in 
1862. Graham pad employed it,as opposed to colloid 3h, Lb w*l p whepy 
be found that Nigeli’s crysta'loids are crystalloid in Grerar 3 sens, 
