278 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



ketecl at a premium over correspond inji; sun-dried materials, and it is 

 believed that in time dehydration will largely replace sun drying, 

 because the dehydrated product is superior and the process under 

 many conditions may be more economical. 



Work was done in cooperation with the Bureau of Markets on the 

 curing of sweet potatoes and assistance has been given in furthering 

 the proper handling of southern sweet potatoes. A report upon the 

 preparation of sweet-potato flour by the methods that are being used 

 with success in the preparation of white-potato flour has been pre- 

 pared for publication. 



Much propaganda has been made to extend the use of dehydrated 

 products, and large quantities of these materials have 1)een dis- 

 tributed to hospitals, asylums, and other interested parties for the 

 purpose of familiarizing the public with these products and of 

 assisting in the creation of a wider market for them. At present the 

 industry needs much information concerning improved methods of 

 preparing the raw material before dehydration, and more knowledge 

 concerning the chemical changes which occur on deterioration is 

 essential. Future work will be concentrated very largely upon these 

 and related problems. 



COLOR INVESTIGATIONS. 



A o-eneral discussion of the work of the color laboratory has been 

 printed in the Journal of Chemical and Metallurgical Engineering. 

 The work of this laboratory has been hampered b}' numerous resig- 

 nations. Though the staff consists of but 12 chemists, during the few 

 years of its existence it has lost more than 35 men, who have left to 

 fill positions in commercial dye plants. The training of these men 

 in itself represents no small contribution to the progress of the indus- 

 try. Toward the end of the year the laborator}^ was moved to the 

 color laborator}^ building at the Arlington Farm, although the build- 

 ing is not yet completely equipped. 



One of the features of the laboratory's work has been the applica- 

 tion of optical crystallographic methods in dyestuff research. These 

 methods have been found of the greatest use in the work to deter- 

 mine the puritj' and character of compounds as well as in other 

 ways. These methods have been introduced to the industry and the 

 bureau's facilities have been placed at the disposal of the industry 

 for the training of experts. 



The work upon photosensitizing dyes has been continued. Krypto- 

 cyanin (Kill), a new dye with a sensitization maximum at 7,400 X, 

 has been prepared in amounts aggregating several grams. Three 

 dyes of this series have been prepared crystalline. Two of these 

 have been tested at the Bureau of Standards and found to be useful, 

 but not equal in sensitizing action to Kill. 



It is reported that more than 100,000 pounds of phthalic anhydride 

 are being produced monthly by the bureau's process and that it is 

 being exported to Europe. "The price has fallen so materially that 

 the annual saving probably runs into the hundreds of thousands 

 of dollars. A list which enumerates some 300 different uses for 

 phthalic anhydride and gives the references to the literature and 

 the names of the compounds will be issued shortly. 



