BtJEEAtr OF CHEMISTEY. 223 



for tlie determination of lead in zinc oxid; upon a new method for 

 the determination of caffeine of general applicability; upon the deter- 

 mination of saccharin; and on the determination by the Kjeldahl 

 method of nitrogen in certain organic compounds. 



The food or drug analyst frequently faces the difficult problem of 

 identifying a substance isolated from complex mixtures in very 

 minute amount and in no high degree of purity. This is especially 

 true in the identification of active principles in the course of the 

 analysis of medicines. The analysts in these cases depend either upon 

 a physiological test or upon more or less vague color reactions. From 

 time to time efforts have been made to introduce the use of the 

 microscope in identifying crystalline materials. Inasmuch as the 

 mere appearance of crystals is not necessarily characteristic, the use 

 of the microscope has been of value only to a limited extent. In 

 recent years methods have been developed for the exact measurement 

 of very minute crystals and also for the determination of the optical 

 properties of such minute crystals. These optical-crystallographic 

 methods hitherto have been applied in the main only to inorganic 

 substances, more especially in mineralogy. It would seem that the 

 same methods might be applied with great advantage in food and 

 drug analysis. Therefore work was undertaken to modify the meth- 

 ods of optical-crystallographic study, as applied to minerals, so as to 

 render these methods applicable to the substances met with in the 

 work of the bureau. Department Bulletin 679, " The Application of 

 Optical Methods of Identification to Alkaloids and their Com- 

 pounds," giving the results of this investigation, was published. 

 Work is now in progress to apply these methods of identification to 

 specific groups of substances, so that in time the optical-crystallo- 

 graphic properties of a large number of substances, the identification 

 of which is required in the course of food and drug analyses, may be 

 recorded. The work upon one such group, the cinchona alkaloids, 

 has demonstrated that these methods are eminently suitable for iden- 

 tifying or distinguishing from one another these closely related bases. 

 The results have been published. 



Incidental to this work, a study has been made upon the possible 

 value of optical properties in tracing the configurations of organic 

 substances. Some interesting results have been obtained and made 

 public. In certain simple cases it was found possible to work out 

 space lattices for organic compounds from a consideration of their 

 optical and crystallographic constants. A note on the fundamental 

 polyhedron of the diamond lattice has been published. 



COLLABORATION. 



The Bureau of Chemistry has. cooperated with the Post Office 

 Department in helping to secure fraud orders against a number of 

 concerns marketing through the mails preparations with fraudulent 

 medicinal claims. A number of frauds emanating from Chicago 

 were suppressed. 



It has also done much work for the Department of Justice. 



The Tariff Board has been assisted in the compilation of data con- 

 cerning imported chemicals and drugs. 



