OF THE A.MKKK AN A< ADKMT. 



I was prepared byeva] .■• ]<> c.c. of solution I repeat- 



edly with nitrio acid and making up to one liter. The bottles were 

 heated daring the redaction in an air bath in each a way that all above 

 tin- necks protruded At G0° the bands obtained from :; e.c. of the 

 dation after thirty minutes of reduction were only about 13 

 ■cut of the standard for 30 mmg. ofarsenious oxide. Parallel trials 

 with :i c.c. of the arsenite solution gave bands uf the standard length. 

 Another experiment at 90° gave no bettor results. The bands from 

 the arseniate solution were not over 50 per cent of the standard, while 

 the parallel arsenite reductions gave shorter bands than at ordinary 

 perature, owing to the larger amount of moisture carried over. 

 That a reduction at the boiling point would cause a practically com- 

 plete conversion to arsine, as claimed by Bird, seems improbable, while 

 the ni' >i-t ure equilibrium would be so disturbed as to invalidate the 

 procedure. 



Returning to the reduction at ordinary temperature, it was found 

 that mi increased effect was produced within the standard time by the 

 addition of stannous chloride or potassic iodide. Platinum in contact 

 with the zinc, even when the acid was more concentrated, was of no 



rice, and the use of copper-covered zinc did not help. An appre- 

 ciable increase but not a complete reduction was effected by sesquisul- 

 phate of titanium. It was evident that the use of a catalytic agent did 

 not solve the problem with such small amounts of 'arsenic, and we 

 were therefore forced to a reduction of the arseniate to arsenite before 

 testing. For this purpose we found sulphurous acid the simplest 

 substance, since comparatively little is needed, no excess of reagent 

 need be left in solution, and it can easily be prepared free from 

 nic. 



The sulphurous acid solution was made from pure copper and pure 



sulphuric acid, and was saturated at <>°. The solution gave no test for 



■nic when tested in quantities larger than would be used in an 



The tests were made after boiling out the sulphur dioxide 



from the samples. 



We ih" efficacy of the sulphurous acid as follows : Four por- 



tions of tl Lie acid solution, corresponding to 10, 20, .">", and 40 



mmg. of arsenious oxide, were evaporated in small glass dishes with 

 6 .-.•■. of the sulphurous acid until the excess of sulphur dioxide was 



apparently expelled. On adding the residues to the reduction bottles, 



color baud- cone up quicklyas in the case of arsenites, and in thirty 



minute- all the bands were equal to the corresponding standards in 



length and intensity of color. Suhsequenl trials conducted similarly 



firmed the The precaution was taken to use the lead 



