550 



SCIENCE 



[Vol. LVI, No. 145^ 



pressure of the casein itself. The observed poten- 

 tial difference tsetween the two solutions in milli- 

 Tolts always has the numerical value equal to 59 

 times the differenee in p^^ value between the two 

 solutions at 24°, proving that the inequality in 

 p value is determined by Donnan 's equation for 

 membrane equilibria. 



A preliminary study of a plunger type of jelly 

 strength tester: S. E. Sheppakd and S. S. Sweet. 

 In previous papers tire authors have described an 

 instrument for measuring in absolute units the 

 rigidity of gelatin jellies. They have used the 

 results to check the performance of plunger tj^pes 

 of jelly strength testers. In these instruments a 

 plunger resting on the jelly is loaded to produce 

 a fixed arbitrary depression or distortion. The 

 authors have devised an instrument with a bal- 

 anced beam, and continuous chainomatic loading. 

 Hence the load : deflection, or stress : strain 

 curves can be plotted for constant rate of loading. 

 The points investigated were: (1) Effect of 

 shape of plunger. It is found that with plungers 

 having a rounded base the area of contact varies 

 with the load, and unreliable load : deflection 

 curves are produced. The most satisfactory 

 plunger is a' frustum of a cone, with the larger 

 base resting on the jelly surface. Families of 

 straight lines passing through the origin are ob- 

 tained in good agreement with Hooke's law. 

 (2) Eatio of diameter of plunger to diameter of 

 vessel. Using plunger heads of above shape, this 

 ratio should be less than a certain value, or 

 spurious rigidity; hence spurious jelly strength 

 will be obtained. This is a function of the abso- 

 lute jelly strength (rigidity) so that comparisons 

 for grading may be vitiated. (3) Eatio of de- 

 pression to height of jelly. Similarly the depth 

 of jelly. must be large compared with the depres- 

 sion, using the same plunger diameter. These 

 results are discussed in connection with recent 

 work on the structure of jellies. 



On the non-isotropic sivelUng of thin sheets of 

 gelatin: S. E. Sheppaed and S. S. Sweet. By 

 coating definite amounts of gelatin solution of 

 various concentrations, etc., on suitably prepared 

 glass plates, after drying flat sheets of definite 

 thickness and area can be stripped off. The 

 swelling of these in water and aqueous solution 

 is not isotropic, i. c., not uniform in all directions, 

 but greatest for the thickness. It is found that 

 the ratio of volume increase to area increase dif- 

 fers for different gelatins, and also depends upon 

 the treatment, becoming lower, for example, on 

 hardening with formaldehyde. 



The preparation of gelatin free from ash and 



Jiydrolytic decomposition products: S. E. Shep- 

 pakd, Felix A. Elliott and Miss A. J. Bene-- 

 DiCT. A 5 per cent, solution of commercial gela- 

 tin is eleetrolyzed in a cell of eleetrofiltros for- 

 three to four weeks, the salts passing through the- 

 cell into the electrode chambers. This reduces 

 the ash to ca. 0.10 per cent. This deaslied solu- 

 tion is then precipitated with acetone, thus re- 

 moving hydrolj'tic decomposition products and^ 

 further reducing the ash to ca. 0.01 per cent.. 

 This gelatin is then redissolved in conductivitj'- 

 water, chilled in sheets and dried. The reaction, 

 of a solution of such gelatin in solution is about 

 4.S H-ion. This gelatin is useful for all research-, 

 work on gelatin as well as providing a definite- 

 material for culture media which can be brought 

 to any pai'ticular reaction -with complete knowl-. 

 edge of salts present. 



The Itygroscopicity of hide gives and the rela-- 

 tion of tensile strength of glue to its moisture' 

 content: E. Bateman and G. G. Town. 



Tlie two forms of gelatin and their isoelectrio- 

 points: John Arthuk Wilson and Erwin J. 

 Kern. In a tenth-molar phosphate solution of" 

 increasing Pjj value, .gelatin shows two points of' 

 minimum swelling, one at 4.7 and the other at 

 7.7. It is suggested that the two points of mini- 

 mum represent the isoelectric points of the get 

 and sol forms of gelatine, respectively. 



Some modern problems in leatlier chemistry:- 

 Edmund Stiasnt. The striking feature of mod-, 

 ern research in leather chemistry is the entirely- 

 different point of view in the choice and treat- 

 ment of problems as compared with the perioii, 

 previous to ten years ago. The older experimenta- 

 tion was entirely from the standpoint of direct 

 practical investigation, while in pure research for- 

 the purpose of deep understanding of the pro- 

 cesses, entirely unfettered by any thought of im- 

 mediate practical utility, in which the entire- 

 structure of modern science is employed, activity 

 has become evident only within the past decade. 

 Professor Procter is the connecting link between, 

 these two eras and the exaniple set by him in his 

 scientific attitude is especially evident in the- 

 United States. A few of the problems of timelj' 

 interest are the chemical nature of collagen, the 

 mechanism of bating and what is called the- 

 astringencj' of "vegetable itannins. (The author 

 reviews the results- of his experimentation upon 

 these problems which will be published in full 

 later). The ultimate aim of all research in 

 leather chemistry is the widening and deepening- 

 of our fundamental knowledge of this as yet 

 very undeveloped field. 



