Several methods of purifying collagen were studied . The effects of particular treatments on collagen were followed by nitrogen determina tions, by electrometric t itra tion analyses, and by electrophor etic measurements.Treatment of the raw material with t rypsin , as in the conventional method for t he preparation of collagen, results in changes t hat lead to a degradation of the collagen in s ubsequent extr actions. Treatment with dilu te salt solut ion followed by trypsin produces a rpaterial of compal'ati vely low isoelectic point (pH 5.5). Apparently soakin g in dilute salt solu t ion is not detrimental to collagen, and it is r ecommended that this type of extraction be sub tituted for t he extraction with trypsin.A technique for removing all but a negligible part of the mineral content from collagen is described, and a pr ocedure is recommended for use in the preparation of ash-free gelatin .A specification is proposed for purified collagen: (1) The water extract shall have a pH range of 6.0 to 7.0 ; (2) the isoelectric point (determined electrophoretioally) shall be between pH 6.0 and 7.5; (3) the material shall have an ash content of less than 0.1 percent, total nitrogen content of 17.8 to 18.1 percent, and au amide nitrogen content (determined by hydrolyzing for 20 hours in 0.1 N hydrochloric acid at 90° C) of at least 3.8 perccnt, expre1'sed as perce ntage of total nitrogen.

The adsorption of water vapor by co ll agen, commercial hide powder, and severa l leathe rs was determined at various relative humidities ranging from about 0 to 96 percent, at 28°, 50°, and 70° C. Determi nations were also made on chestnut a nd quebracho tann ins at 28° C at vari o us re lative humi dities. The results indicate that at 50-percent relative humidity the vari ation of moisture conte nt for 1 degree change in temperat ure is e quivale nt to t hat for 1 perce nt cha nge in relative hum id ity. A specia ll y pu rifi ed co llagen h as higher affinity for wate r tha n does hi de powder, showing that t he pr evio us chemi cal treatment in fluences adsor ption. The res ults obtain ed from t he exp eriments 011 t he tan nin s a nd t he h ide powder show that tanning does not decrease water vapor adsorptio n at relative humiditie below 70 percent.F rom t he resu lts of t he adso rption measureme nts, heats of adsorption we re calcul ated by m eans of t he Cla usius-Clapey ron and Brunauer, Emmett, and Teller eq uations. The leathe rs sh ow hi g her heats of adsorp tion for low moist ure regains th an does co llage n, indi cati ng that they co ntain so me g roups t hat a re more highly act ive' towa rd wate r tha n t hose in coll agen . F ree e ne rgy and e nt ropy values for the adsorption at 50° C are given. The efi'ect of hi g h temperat ures o n moisture adsorption is studi ed by su bjecting specimens to elevated temperatures and t he n determ ining th e adsorption at 28° C. Methods are give n for estim ating m oist ure eo ntent for conditions t hat have not been st udied expe rimentall y. T he change of wate r adso rption wit ll tempe rat ure can be expressed by a simple relation involving th e log of the perce ntage of water adso rbed and t he inverse of the absolu te tempe ratu re.

Lactic, citric, hydroxyacetic, and gluconic acids were found satisfactory for stabilizing iron solutions to be used for tanning leather. The influence of pH and concentration on the combination of iron (F e20 a) with standard hide powder was investigated. The maximum fixation of 23 t o 25 percent of ferric oxide occurs in t he pH range 3.5 to 4.0. Practical tanning experiments were made with goat-and calf-skins. The shrinkage temperatures of the iron-tanned leathers are lower than those of well-tanned chrome leathers. The results of accelerated a ging test s indicate that all of the iron-tanned leathers tested had at least fair aging qualities except where gluconic acid was used. The use of iron salts for replacing those of chromium in the tanning of leather shows most promise where citric acid is used for stabilizing the solutions.

No abstract

AdsOJ'ption of water vapor by untanned hide and variou tannages oJ leather was determined at relative humidities rangin g from 0 to 96 percent at 100° F. The Brunauer, Emmett, and T eller equations for adsorption of gases in multimolecular layers we re applied to the data. Adsorp1ion for all of the samples below a re lative humidity of 75 percent is a function of the available surface. Above 75-percent relative humidity, other factors exert an influence, the most importan t of which is probabl.v size of the capillaries. Untanned hide and chrome-tanned leath er adsorb the most water vapor except at relative humidities above 75 p ercen t, at which sol e leather adsorbs more. The behavior of the sole leather in this r egion is ascribed to the prese nce of deliquescent materials used in the fini shing process. The other vegetable-tanned leather s adsorb less mois ture than either hide or chrome leather. Calculated heats of adsorption indicate t hat the affinity of groups for wate r is no t appreciably altered by tanning and t hat the adsorption is physical in nature. M ethod by which the data may be applicd to practical processes, s uch a s fa t-liquoring and tanning, are pointed out.