

METHOD OF DETERMINING ARSENIC. 27 



part of the tube where the mirror is deposited is cut off, carefully 

 wiped and placed in a desiccator. It is then weighed on an assay 

 balance capable of weighing to the fifth place. After this the tube is 

 dipped in a sodium hypochlorite solution to dissolve the arsenic, 

 washed with distilled water, then with alcohol, and finally with ether, 

 dried, placed in a desiccator, and weighed again. The difference in 

 the two weights represents the arsenic from the amount of material 

 taken. Both of these weighings must be made with the utmost care, 

 as a small error at this point will cause a large error in the result. 



STANDARD SOLUTION. 



The standard solution from which the mirrors are prepared is made 

 in the following way : Dissolve 0.0855 gram of dry C. P. arsenious 

 oxid in a sodium bicarbonate solution (free from arsenic) by boiling, 

 weakly acidify with sulphuric acid, and make up to 1 liter. Each cubic 

 centimeter of this solution contains 0.0855 mg of arsenious oxid, 

 equivalent to 0.0648 mg, or 0.001 grain, of arsenic, and is used to pre- 

 pare the standard mirror of .0.001 grain. Place 15.4 cc of this solu- 

 tion in a 100 cc flask and add water to the mark. Each cubic 

 centimeter of this solution represents 0.01 mg of arsenic. Aliquot 

 portions are used for making the remaining standard mirrors. 



REMARKS. 



The extra apparatus for generating hydrogen, such as is described 

 by Sanger in his article, was not used. It was found that by placing 

 the hydrogen-generating flask in a casserole of cold water the rate of 

 flow could be very nicely regulated. A Liebig potash bulb containing 

 lead acetate solution was also placed in the series. This was to rid 

 the gas of any of the hydrides of sulphur, selenium, or tellurium that 

 might be formed and afterwards broken up by heat and deposited 

 with the arsenic. No trouble was experienced in recovering all 

 arsenic, even though the arsin had been passed through a lead acetate 

 solution, since the tremendous flow of hydrogen, as compared with 

 the arsin, drove all of this substance which might have been dissolved 

 during the first part of the determination out of the solution before 

 the operation was completed. 



DESCRIPTION OF SAMPLES AND ANALYTICAL RESULTS. 



In Tables V to XIII are given the data in regard to the samples col- 

 lected, their description, price, the country in which manufactured, 

 and the analytical results obtained as to arsenic content, expressed 

 both in grains per square yard and in milligrams per square meter. 

 Table V contains the results of the examination of wall papers. 



