60 



promoted if the size were added to the beater before the alum. In 

 an actual test, worldng in this order, the paper tested 1| points higher 

 than that made by putting the alum into the beater first. 



Photographic workers sometimes experience a most annoying 

 reticulation of the surfaces of negatives, particularly when fixjng or 

 washing during hot weather. The wet gelatin layer becomes finely 

 wrinkled or corrugated, the network of puckers forming a pattern. 

 Sheppard and Elliott have found two causes for this difficulty. 

 When sheets of gelatin swell or contract slowly, they undergo a 

 change in volume but not in shape. On tlie other hand, the gelatine 

 on a negative must undergo a change in shape, since one face of 

 it is held to the plate. So long as the amount and rate of swelling 

 are not great, no trouble is experienced, but when the swelling is 

 excessive, due to higher temperatures or chemicals in the fixing bath, 

 the upper surface of the gelatin will have an area so much greater 

 than the lower surface as to cause puckering. The second cause is 

 the presence in the solution with which the plate is treated of both 

 swelling and contracting agents. Reticulation is readily produced by 

 immersing the plate in a solution containmg acetic and tannic acids, 

 the former tending to swell or soften the gelatin, the latter to 

 contract or harden it. Their rates of diffusion are determined b}^ 

 their effects upon the gelatin, and the result is a mosaic-like alternation 

 of hardening and softening effects, the ridges being more swollen and 

 the valleys contracted by tanning. 



Judging from the Hterature available, the most extensive 

 applications of imbibition have been in the field of biology. Almost 

 without exception, this has been done by analogy, rather than by 

 application of theory. Fischer's book, " Edema and Nephritis " is 

 replete with analogies between inhibition of such proteins as gelatin, 

 fibrin, and gluten, and that of things so widely different as muscles, 

 eyes, nervous tissues, catgut, and Uving frogs. Loeb showed that 

 the laehaviour of dried pig's bladder in solutions of various salts very 

 closely resembles that of powdered gelatin in the same solutions. 

 Reference should also be made to Loeb's work on the fundulus egg, 

 to Arnold's studies of the sweUing of human muscle, and Traube's 

 work on the swelling and germination of plant seeds. 



Recent Publications Dealing with the Application, or Suggesting an Application* 

 of the Subject of Imbibition of Gels. 



(See also Bibliography at end of Part I.) 

 Arnold, R. ' The Swelling Capacity of Different Kinds of Muscle in Acid 

 Solutions.' ' Kolloidchem. Beihefte,' 5, 511 (1914). The structure of human 

 muscle is not a criterion of its relative swelUng capacity. 

 BovAUD, W. M. ' CoUoidal Chemistry in Papermaking.' ' Paper ' 22, 11 (1918)- 

 Shows the importance of controlling hydration of the stock in making paper. 

 FiscHEE, M. H. ':Relation between Chloride Retention, Edema, and " Acidosis." 

 'J. Am. Med. Assn.' 64, 325 (1915). 



' The Classification and Treatment of the Nephritides.' ' The Journal- 

 Lancet,' July 1, 1916. 

 Fischer, M. H., and Hooker, M. O. ' Trench Nephritis.' ' The Int. Assn. of 

 Med. Museimis,' BviUetin No. VII., May, 1918. 



' Ternary Systems and the Behaviour of Protoplasm. ' Science, 48, 143 

 (1918). Many of the laws governing the hydration and dehydration of soaps 



