THE PURITY OF THE FUSED ARGENTIC NITRATE. 63 



tated by somewhat concentrated alkali does not quickly redissolve in an 

 equivalent quantity of nitric acid, mixed with the dilute argentic solution. 

 It was found that even the precipitate caused by 0.1 ml. of a two-hun- 

 dredth normal solution may produce a fairly permanent cloud in spite of 

 the presence of an excess of 0.00003 gram of nitric acid, enough to dis- 

 solve it. Still more dilute solutions behaved much more satisfactorily, 

 however. A milliliter of a two-thousandth normal caustic solution (equiv- 

 alent to 0.00003 gram of nitric acid) added with constant stirring to the 

 pure standard argentic nitrate formed a cloud easily seen in the neph- 

 elometer. In case 0.00003 gram of nitric acid had been introduced 

 before adding alkali, no precipitate was formed under the same conditions. 

 Hence under these circumstances the test attained a degree of sensitive- 

 ness suited to the case in hand. 



In this way it was found that the argentic nitrate remaining from syn- 

 thesis 11 gave a distinct opalescence with the addition of 0.00002 gram of 

 sodic hydroxide, and an obvious cloud with 0.00003 gram. Hence it was 

 concluded that argentic nitrate fused in a stream of pure air for one hour 

 contains no weighable excess of nitric acid. 



The various suspected impurities having thus been duly sought, it is 

 instructive and interesting to tabulate the results. These are as follows : 



Grams 



Weight of fused AgNOs from 100,000 grams Ag 157.480 



Correction for weight of 



Dissolved air 0.000 



Retained water 0.0016 



Retained ammonic nitrate 0.0007 



Nitrite 0.000 



Free acid . 0.000 



Corrected weight of argentic nitrate obtainable from 



100.000 grams of pure silver 157.478 



As the subtractive corrections given in the above table are maximum 

 values, the weight of argentic nitrate in question can hardly be lower than 

 this value, 157.478. On the other hand, it can hardly be higher than the 

 uncorrected value, 157.480. Thus two limits are set, very near together, 

 between which the true value must lie. Obviously, for the present one 

 can not go very far astray in accepting the mean value, 157.479 ; and this 

 value will be used in the following discussion. 



