.-z
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INDUSTRIAL AND ENGINEERING CHEMISTRY
against L, when the intercept on the L axis will be the ultimate loss and the intercept on the LIT axis will be l / a or the initial loss rate.
Conclusions An empirical equation has been found which, except for a short initial period, represents the amount of oil pressed from a grease in a given time by the Herschel grease press. The ultimate oil loss for various pressures has been cald a t e d by means of the oil-loss equation for a number of greases. The viscosity of the petroleum oil contained in a grease has been shown to effect materially the initial oil-loss rate without changing the ultimate oil loss for greases of the same consistency. Increasing the pressure applied to a grease increases the initial oil-loss rate and also increases the ultimate oil loss.
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The nature of the soap base used for compounding greases has been found to exert an influence on the amount of oil capable of being pressed from the grease. The mineral oil tends to be more firmly held by the smaller soap fibers, although other factors such as mineral oil content and oil viscosity predominate under certain conditions. The bleeding characteristics of greases have been correlated with the initial oil loss in the Herschel grease press.
Literature Cited (1) Farrington, B. B., and Davis, W. N., IND.ENQ.CHEM.,28, 414 (1936). (2) Herschel, W. H., Proc. Am. SOC.Testing Materials, 33,Part I,343 (1933). RECEIVED October 17, 1938. Presented before the Division of Petroleum Chemistry at the 96th Meeting of the American Chemical Society, Milwaukee, Wis., September 5 t o 9, 1938.
BLEACHED LAC Factors Which Influence the Keeping Quality N. N. MURTYl The Indian Lac Research Institute, Namkum, Ranchi, India
A
GE leaves its indelible mark upon bleached lac even
before the resin has lost its original solubility. A study of commercial bleached lac has shown that freshly bleached lac dissolves without much previous swelling, but that aged samples which have been stored swell and then form a jelly before dissolving. The time interval which elapses between the introduction of the dry bleached lac into the solvent and the obtaining of a homogeneous solution has been referred to as the “gelatin period.” It has been found to vary with different commercial lacs (10) and to depend upon the age and quality of the sample. Many samples of aged lacs gave highly viscous and slowly filtering solutions. A few exhibited these characteristics to an abnormal degree. All these changesindicated that during the period of storage the bleached lac micelle had increased in size, probably through polymeri~ationor aggregation. It had not been definitely experimentally established, however, whether this phenomenon is attended by a change in chemical composition of the resin. Nagel and Kornchen (3) believe that the chlorine present in bleached lac splits off as hydrochloric acid during storage and that this mineral acid acts as a catalyst to bring about aggregation of the resin molecules. Bhattacharya and Verman (1) postulate that hypochlorous acid coordinates with an oxygen atom of possible ether linkages in the shellac molecules during bleaching and splits off during the storage, freeing valencies of the oxygen atom which are saturated by polymerization. It would appear in either case that the chlorine present in the bleached lac was responsible for the gradual formation of insoluble resin. More highly chlorinated bleached lacs in general showed the greater percentage of insoluble resin after they had been stored and examined in the author’s laboratory, but a considerable 1 Present address, Metropolitan-Vickers Electrical Company, Ltd., Trafford Park, Manchester. England.
number of high chlorine content nevertheless retained their solubility better than those of lower chlorine content. It would appear, then, that there are other factors which influence the rate of deterioration of the lac. It was therefore the purpose of this investigation to determine the extent t o which various factors influenced the keeping quality of
Bleached lacs constitute one of the most widely used group of resins for light-colored quick-drying finishes, in spite of the fact that they are comparatively perishable, lose their solubility in alcohol, and darken in color when stored under ordinary conditions. Nothing has been written of the many efforts which have been made to improve these products, since even general details of the bleaching process have been, until recently, kept as secrets of the industry. Consequently, there has been a great deal which consumers have not properly understood and appreciated in the use of these resins. A n effort is made in this article to acquaint the reader with the factors which in the bleaching of lac have an effect upon the keeping quality of the product.
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lesced on heating but did not have a measurable life period,
TABLEI. RELATION BETWEEN LIFE UNDER HEAT,INSOLUBLES,the samples were considered as having a life of 2 to 3 minutes. .4ND
Sample 1 2
Life at 140' C. Min.
