350 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



the serviceability of canvas may be doubled by proper treatment to 

 protect it against moisture and sun. 



The result of the investigation on the effects of waterproofing 

 materials and outdoor exposure upon the tensile strength of cotton 

 yarn showed that after exposure to the weather for one year the 

 treated yarn was in most cases stronger than the untreated yarn after 

 exposure. Exposure tests on cotton duck given the same and similar 

 treatments indicated that the results on yarns are not strictly 

 applicable to the woven fabric, since the treated canvas after ex- 

 posure is usually weaker than the untreated canvas after exposure. 

 An important investigation was completed on the effects of materials 

 used in waterproofing and of outdoor exposure to the weather on the 

 tensile strength and water resistance of canvas. The conclusions 

 drawn from the investigation are that the addition of certain 

 mineral pigments to waterproofing preparations is beneficial, since 

 they reduce the weakening effect of solar light and heat without 

 reducing the water resistance. 



Investigations in cooperation with the Connecticut Agricultural 

 Experiment Station and the Connecticut Valley Tobacco Improve- 

 ment Association are now in progress to develop methods for treating 

 tobacco shade cloth so that its serviceability may be materially in- 

 creased. It is believed that the final results of this investigation, 

 which is being conducted both in the field and in the laboratory, will 

 be useful in increasing materially the life of tobacco shade cloth. 



UTILIZATION OF CULL AND SURPLUS SWEET POTATOES. 



Great areas in the Southern States are peculiarly adapted to the 

 growing of sweet potatoes which, if produced with a reasonable 

 assurance of profit, would serve a useful piirpose in developing 

 diversified farming in the South. The possibility of increasing the 

 profitable production of sweet potatoes depends upon the develop- 

 ment of a demand for sweet -potato products. Thus far it has been 

 impossible to develop a market to an extent commensurate with the 

 production possibilities. The technology of converting sweet pota- 

 toes into salable food products is a problem to which the bureau has 

 given much thought and energy. 



A laboratory investigation has shown that, upon cooking, sweet 

 potatoes change from a starchy into a saccharine foodstuff which is 

 largely maltose sugar, one of the most nutritious and digestible of 

 the carbohydrates. It was found that the diastatic power of dried 

 sweet-potato tissue is three or four times that of the best distillers' 

 malt. This suggests the possibility of the development of an indus- 

 try for the production of sweet-potato flour to be used because of its 

 high diastatic power in bread making and in other ways. 



Experirnental work showed that the sweet-potato diastase has 

 three striking properties: (1) It has less liquefying power than malt 

 diastase; {2) it does not attack the complexes in the starch molecule 

 as uniformly as does malt diastase; (3) it works at a higher tem- 

 perature than malt diastase. Work on the technical significance of 

 these properties is now under way. 



The results of experimental work on the manufacture of sirup 

 from sweet potatoes are published in Department Bulletin 1158, 

 Production of Sirup from Sweet Potatoes. 



