BUREAU OF CHEMISTRY. 5G9 



studies have been mrule on the toxicity of caffein with special refer- 

 ence to certain factors modifying toxicity, such as starvation, varia- 

 tion of temperature, and fatigue. This research is nearing comple- 

 tion. The toxicity and elimination of caflfein under some pathological 

 conditions, as after removal of the kidneys, were studied in rabbits. 

 The results show increased excretion of catfeinby the gastro-intestinai 

 epithelian under this condition, but the toxicity of caffein is not 

 markedly affected and is not cumulative. The action of caffein on the 

 circulation, with s]:»ecial reference to drugs modifying its effect, has 

 been studied extensivelj'. 



The pharmacological action of tin was begun, but little progress has 

 been made. 



Physiological tests were made with samples of spoiled cheese as to 

 the presence or absence of a toxic substance, but the results were nega- 

 tive. Tests were also made upon " Ricin Preparat" which was being 

 used in an assay method for the determination of pepsin, with a 

 view of ascertaining its degree of toxicity. 



Samples of digitalis leaves, as well as medicinal preparations, were 

 tested ; some of the latter were found to be of only fair quality and 

 others were fully up to the standard. 



CHEMICAL REAGENTS. 



During the year 392 samples of chemical reagents supplied to the 

 Bureau of Chemistry and branch laboratories on contract have been 

 examined. Improvement is noted in the quality of chemicals supplied 

 this year over that of those supplied the previous year. In a few in- 

 stances, however, the bureau has had some difficulty in obtaining 

 " special reagents " that will comply with their specifications and that 

 will be of a degree of purity necessary for the special analytical work, 

 although the manufacturers have worked in hearty cooperation with 

 the bureau in its efforts to obtain the desired chemicals. Among these 

 can be mentioned " special " acetic acid, 99.9 per cent pure, of which 

 frequent rejections were made, either because the product did not com- 

 ply with the sulphuric acid-bichromate test or because it was low in 

 strength. Hydrochloric and nitric acid were also found to be unsatis- 

 factory because of the presence of arsenic. 



There has been urgent demand recently from various laboratories 

 for mineral acids and zinc that are more nearly free from arsenic 

 than those supplied up to this time for special investigations where 

 exceedingly delicate tests were being employed. The bureau has had 

 no difficulty in obtaining sulphuric acid which is practically free from 

 arsenic, but it has experienced great difficulty in obtaining hydro- 

 chloric acid and nitric acid free from arsenic. The bureau is now 

 experimenting with ceresin bottles to note the arsenic content of nitric 

 acid delivered in such bottles. It has been practically impossible to 

 obtain zinc absolutely free from arsenic. The reagent laboratory is 

 investigating a method of testing for arsenic in its reagents by a 

 modification of the Gutzeit test, in which electrolytic reduction is 

 em]iloyed. thus eliminating the use of zinc and using as the electrolyte 

 sulphuric a'"id, which is itself relatively free from arsenic. 



Among the rejections made during the year may be mentioned the 

 following: 



