274 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



Photosensitizing dyes. — These dyes are used in photographic work, 

 especially in aerial and astronomical photography. Improvements 

 have been made in the preparation of a number of these dyes. A new 

 method for making the dye known as '' dicyanine "' was discovered 

 and a public-service patent applied for. 



New mudytical method. — The greatest need of the dye industry at 

 the present time is for better methods of analyzing dyes and inter- 

 mediates used in preparing them in order to produce dyes that will 

 give uniform results. Work along this line was undertaken and a 

 new method devised for the detection of " H " acid, a substance used 

 very extensively in the dye industry. A full description of the 

 method was published in one of the technical journals. 



Physiccd chemical tneasurements. — Inasmuch as no reliable data 

 were available on certain physical constants of the more important 

 intermediates, work was undertaken for their determination. Vapor 

 pressure measurements were made on naphthalene, anthracene, phe- 

 nanthrene, and anthraquinone. The solubility of certain naphthalene 

 sulphonic acids which are used in the dye industry was determined. 



Sta7idardization of hiologiccd stains. — A chemical study of the pre- 

 war German biological stains and of the American product which is 

 being manufactured to take their place, with rather unsatisfactory 

 results in some instances, was undertaken. Inasmuch as these stains 

 are used by bacteriologists, pathologists, physicians, and veterinarians 

 in the study and identification of disease-producing organisms, it is 

 of the greatest importance that only stains of uniform and constant 

 composition be used for such work. This problem is of importance 

 to the countr}'. inasmuch as the health of the citizens and also the 

 health of the live stock and plant crops of the country are vitally con- 

 cerned. In view of the rather extensive nature of the problem, only 

 the most important of the biological stains were investigated during 

 the year. It was found that certain American stains were equal to 

 the pre-war German stains, whereas others were unsatisfactory. The 

 methods for preparing these stains are being thoroughly investigated 

 and an effort made to standardize the methods of preparation so as 

 to obtain a uniform product. This work is being pushed rapidly and 

 the possibility of devising quick and accurate analytical control 

 methods is being investigated. 



Production of thymol from cymene. — Thymol is a drug that is used 

 extensively as an antiseptic, but more especially as a specific against 

 the hookworm disease. It is now imported from India, where it is 

 found in the seed of one of the plants indigenous to that country. 

 It was discovered, however, that synthetic thymol identical with 

 the natural product can be obtained from cymene, a waste product 

 in the paper industry. It is estimated that 2.000,000 gallons of 

 cymene are w^asted annually in this Country and Canada. Thymol 

 is now sold for $4.50 per pound, whereas it is estimated that the 

 synthetic product can be made for about $2.50 per pound. A public- 

 service patent on the process has been applied for. Several chemical 

 manufacturers have already become interested in it. and it is quite 

 likely that tliis country will soon be able to produce all the thymol 

 consumed here. 



Certification of dyes. — The work on the certification of dyes is done 

 in the analytical section of the laboratory. This is part of the food 

 and drug enforcement work. A certain limited number of dyes are 



"to 



