186 



SCIENCE 



[Vol. LV, No. 1416 



sulfuric acid and their ratio one to another. The 

 researches by "Wilson and Kern, of Milwaukee, 

 and by this laboratory have demonstrated that 

 many simple substances hitherto considered -with- 

 out any influence may have a profound effect on 

 the process of chrome tanning. In this research 

 effects of the substances mentioned in the title 

 have been carefully studied and a chemical theory 

 has been propounded which involves the forma- 

 tion of addition compounds. The recognition of 

 the existence of such compounds will be required 

 for proper control of chrome tanning. 



Differentiation between physical mixtures and 

 chemical compounds: Jeeome Alexander. 



Effect of acidity upon the rate of diffusion of 

 tan liquor into gelatin jelly: John Arthur 

 "WhiSON and Erwin J. Kern. As ordinarily used 

 in tanning, gambler and quebracho extracts show 

 marked differences in the rate of tanning and of 

 penetration into the hide. It is shown that the 

 rate of penetration is a function of the hydrogen- 

 ion concentration as well as of the nontannin con- 

 tent. A sample of gambler penetrated the jelly 

 only at pH values above 3.0, but a sample of 

 quebracho only at pH values above 4.7. Above 

 9.0 the quebracho penetrated more rapidly than 

 the gambler. The shape of the interface between 

 a tan liquor and gelatin jelly was also found to 

 be a function of the hj'drogen-ion concentration. 

 Theory and use of electrometric titrations: 

 Harold Fales. 



The chemical constituents of shin : F. L. Sey- 

 mour-Jones. Animal skin consists of proteins, 

 fats and mineral salts, but for the tanner only 

 the former are of much importance. Proteins 

 occur in nature in the colloid state, a state of 

 matter hitherto somewhat obscure in that it ap- 

 peared impossible to apply normal chemical laws 

 thereto. Professor Procter, of Leeds, and his 

 collaborators, in particular Mr. J. A. Wilson, for 

 many years studied the swelling of gelatin in 

 acids and finally succeeded in showing that it 

 followed a definite course which could be repre- 

 sented by mathematical expression. Dr. Loeb, of 

 the Koekefeller Institute, has carried this further 

 in studying the effects of different acids, alkalies 

 and salts on gelatin and other proteins, and has 

 shown that, taking into consideration the hydro- 

 gen-ion concentration (hitherto neglected), pro- 

 teins really follow ordinary chemical laws. Of 

 the proteins of hide, the most important is col- 

 lagen, which is undoubtedly closely allied to 

 gelatin. Elastin is most stable, but for light 

 leathers is generally removed in the bating 

 process. It is highly elastic under very small 



stresses. For keratins the tanner has little use, 

 and their removal is one of his objects. The 

 interfibrillary cementing substance is usually re- 

 moved in liming; it is probably a mucoid, but its 

 exact nature is still doubtful. A thorough knowl- 

 edge of the chemical constituents of skin is essen- 

 tial if progress is to be made in the science of 

 tanning. So far progress has been slow in this 

 direction, but each advance materially aids in 

 increasing knowledge and possibilities of further 

 advance. 



The warble fly problem: Alfred Seymour- 

 Jones. The warble fly is one of nature's pests, 

 ruining hides by its numerous perforations. The 

 fly lays its eggs on the hairs on the legs of cattle ; 

 from here the maggot hatches and bores into the 

 animal 's body. In order to prevent or cure this 

 plague, the English, Scottish and Irish agricul- 

 tural authorities set up a scientific committee to 

 deal mth the question. Squeezing the warble 

 bots out of the backs of a herd of isolated cattle 

 during five years proved successful, but this 

 would scarcely be feasible on a large scale. Next 

 a mixture of bird lime material and birch tar oil 

 was painted on the hind quarters of some cattle, 

 but, though this might have prevented the flies 

 from laying their eggs, the cattle's tails stuck to 

 the tacky material and they stampeded. A great 

 varietj' of mixtures, to be applied to the cattle's 

 backs when the maggots are nearly ready to 

 emerge, have been tried. Some give 80 to 96 per 

 cent, kills, but the work is as yet incomplete. 

 However, applied to all cattle in an area for two 

 or tliree years, there is reason to hope that the fly 

 might be exterminated. 



Properties and action of enzymes in relation to 

 leather manufacture: J. T. Wood. Enzymes do 

 not merely accelerate a change already in prog- 

 ress, but actually cause it. An explanation is 

 given of Armstrong's view of the two-fold action 

 of enzymes. The action of hydrolytic enzymes 

 is caused by the increase of hydrogen-ion or 

 hydroxide-ion concentration at the surfaces of 

 their particles. The action of enzymes in the 

 various processes of leather manufacture was 

 discussed. In the "soaks" enzymes are secreted 

 by a variety of species of bacteria, as is also the 

 ease in the "limes," but the possibilitj' of the 

 presence of tissue enzymes in these two processes 

 should not be overlooked. The enzymes of the 

 dung bate are then enumerated and a short 

 account of the introduction of commercial enzymes 

 is given. The action of tryptic enzymes on the 

 elastin of the grain and Wilson's experiments are 

 brieflv discussed together with the author's views 



