March, 1923
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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rating by calling that in the enzyme solution a t 40" C., 75 per cent, that in the blank a t 40" C., 50 per cent, and that in both blank and enzyme solutions a t 25" C., 25 per cent. Evidently, the pretreatment of skin with ammonia, which is itself an unhairing agent, does not assist the unhairing action of pancreatin nearly so much as pretreatment with materials that merely swell the skin.
removal. Fig. 1 corroborates this view; where the hair loosening has been effectedby a pancreatin solution a t 25" C., exposed to air, the epidermis has been disintegrated and the hair separated from the skin, but the elastin fibers remain undissolved. At 40" C. a pancreatin solution, such as those used in these experiments, was found to dissolve the elastin fibers completely from unhaired calfskin in about 7 hrs. I n the unCOMBINED BATING AND UNHAIRING ACTION hairing experiments, where the pieces from the enzyme soluThe work of Wilson and Daub indicates that the funda- tions a t 40" C. had not previously been swollen in acid or mental action of bating is the removal of elastin fibers from alkali, microscopic examination showed that all the elastin the skin. We therefore measured the extent to which the had been dissolved away from the flesh side of the skin, but pieces of skin were bated in the pancreatin solutions by ob- none from the elastin layer near the epidermis. The hard servation under the microscope. The two sections shown corneous layer of the epidermis had apparent,ly acted as a were cut a t 30p, stained with logwood and bismark brown to membrane impermeable to the enzyme. I n the ordinary make the elastin fibers stand out prominently wherever methods of unhairing, such as liming, the unhairing agent present, and photographed through a Wratten filter, H acts upon the cells of the Malpighian layer which lie between (blue-green), using an 8-mm. objective and a 5x eyepiece. the corneous layer and the derma. The impermeability of When the pancreatin method of unhairing is used com- the corneous layer to the enzyme explains why the panmercially the liquors are left exposed to air. Our experi- creatin did not attack the Malpighian layer and loosen the ments show that the hair loosening can then be effected a t a hair. I n acid or alkaline solutions, the corneous layer swells temperature of 25" C., but that the action is apparently not considerably and is thereby rendered more permeable. That due to the enyzme, since it is checked by covering the solu- it is also attacked by the enzyme when in the swollen condition tions with toluene. But if pancreatin is not the active agent, is indicated by the fact that no corneous layer could be found we should expect the action not to be accompanied by elastin in some of the sections examined. ~~~~
Total and Available Calcium Hydroxide in Hydrated Lime' By A. S. Behrman and F. R. Porter INTERNATIONAL F I L T E R
T HAS BEEN customary to evaluate hydrated lime for water softening by its total content of calcium hydroxide. Experience in the use of hydrated lime in water softening has shown that the quantity of calcium hydroxide actually available and taking part in the water-softening reactions is frequently not the same as the total quantity of calcium hydroxide determined by the usual methods. This discrepancy is due to a number of factors, chief among which are the limited period of enforced intimate contact of particles of lime with the water being softened; the coating of the lime particles, either with a shell of the carbonate resulting from air slaking, or, during the first few minutes of the softening process, with the insoluble products of the reaction; the rate of settling of the lime particles; and the physical nature of the lime particles themselves. The purpose of this note, and the paper of which it is a condensation, is to point out that hydrated lime to be used for water softening should be purchased on the basis of available, not total, calcium hydroxide content; and the plea is made for a method of analysis which will give a result more comparable with the actual value of the hydrated lime for water softening than the usual procedures employed. The following method of analysis is suggested as approximating conditions encountered in water softening. The data so far obtained are very satisfactory; but time has not been available to accumulate sufficient evidence to prove the general applicability of the method. It is published a t this t h e , therefore, merely as a suggestion, since the authors will be unable for some time to do any further experimental work on this method, or on any desirable modifications thereof which may be developed. I n the method suggested the calcium hydroxide converts
I
1 Condensation of paper read before the Division of Water, Sewage, a n d Sanitation a t the 64th Meeting of the American Chemical Society, Pittsburgh, P a , September 4 to 8 , 1922.
CO , C H I C A G O ,
ILL.
sodium bicarbonate to sodium carbonate. One gram of the unscreened hydrated lime is mixed with about 100 cc. of boiled distilled water, and allowed to stand several hours to insure the precipitation of magnesium as magnesium hydroxide. If time does not permit, however, the precipitation may be hastened by heating the mixture for 30 min. a t or near the boiling temperature. To the cooled mixture are now added 400 cc. of approximately 0.1 N sodium bicarbonate, made just neutral to phenolphthalein. The whole is then shaken or stirred for 15 min. and allowed to stand for 33/4 hrs. The mixture is then filtered, and 50 cc. of the filtrate are titrated with 0.1 N hydrochloric acid, using phenolphthalein as an indicator. The number of cubic centimeters of acid times 7.4 equals the per cent of calcium hydroxide. There are indications that the alkalinity due to residual calcium carbonate involves an error of less than 0.5 per cent and so may be neglected. It is probable also that the preliminary period of contact of the lime with pure water may be omitted, and the lime may be added directly to the sodium bicarbonate solution. We have also contemplated a shaking or stirring period of 1 hr. followed immediately by filtration and titration of the filtrate. This method simulates actual conditions encountered in water softening to the extent that the digestion is made with an alkaline solvent, and that there is formed an insoluble product of reaction. The suggested method yields a filtrate containing an excess of sodium bicarbonate. This is not as truly typical as if a slight excess of calcium hydroxide were present. The advantages of the excess of bicarbonate are that the indefiniteness of the calcium hydroxide-sodium carbonate equilibrium is avoided, the solution may be handled without extreme precautions to avoid absorption of carbon dioxide, and the calculation of the results is extremely simple.
