258 BAXTER, WEATHERILL AND SCRIPTURE. 



In experiments where the foregoing method of determining the glass 

 was employed (Series I and II) a negative correction of 0.20 mg. has 

 therefore been applied. 



Since we found that silicate solutions, of the concentration obtained 

 in these analyses, when acidified with one per cent nitric acid remain 

 clear indefinitely, the experiment was tried of washing the glass frag- 

 ments and the filter paper with nitric acid of this concentration. 

 Somewhat to our surprise not only did the excess in weight of the ash 

 disappear, but a slight deficiency was found. Since this deficiency 

 was practically the same whether or not a glass bulb was involved, it 

 is apparent that some of the mineral constituents of the filter are ex- 

 tracted by either the alkaline silicate or the nitric acid. 



The following table gives the results obtained in blank experiments 

 in which one per cent nitric acid was used as washing liquid. 



Without glass bulb 



With glass bulb 



Average 



The method of filtering the sodium hydroxide solution of the silicon 

 chloride through the filter and then washing the glass and filter with 

 one per cent nitric acid was followed in all the analyses of Series III, 

 and in Analyses 21 to 25 of Series V. In these experiments an average 

 positive correction of 0.07 mg. was applied to the weight of the glass 

 before subtracting the weight of the filter ash, 0.11 mg. 



In all the analvses of Series IV and Analvses 26, 27 and 28 of Series 

 V, the glass was washed with one per cent nitric acid, but a different 

 variety of filter was employed. Blank experiments with these filters 

 gave the following results: 



Excess 

 mg. 



Without glass bulb . 05 



0.03 



