191 



Assay of Saltpetre. 



[April 



the surface water poured off as before, draining off the water to the 

 utmost, with care and attention, in pressing the nitre remaining in 

 the vessel with a tea spoon. 



The nitre remaining in the glass vessel is then to be spread upon 

 a treble fold of filtering paper placed upon a box containing chalk 

 or ashes or any absorbent matter, carefully removing every parti- 

 cle of nitre from the glass vessel ; the box is to be placed in a 

 dry place for 24 hours, the time necessary for the paper &c. to 

 imbibe great part of the moisture — the nitre must then be care- 

 fully removed from the paper with a spoon and a knife or spatula 

 and placed in the same glass vessel in which it was washed to be 

 placed a bed of sand over a gentle fire, aud the salt constantly 

 stirred with a glass rod, till the salt no longer adheres to the rod or' 

 to the vessel, when it will have fallen to a fine dry powder. 



It only remains to ascertain the exact loss in quantity by weigh- 

 ing the nitre recovered, and to the number of drains found wanting, 

 add one per cent for insoluble matter, such as sand or earth, and 

 the amount will be the quantity of impurity contained in the sample 

 of 100 drams, and of course in the whole mass of grough saltpetre 

 received of which it was a part. 



Should the result of the assay shew a loss of weight of 60 per 

 cent, it will be necessary to wash the sample a third time with half 

 a pint of the saturated solution, which would be more than suffici- 

 ent to dissolve the whole that remains of the sample should it prove 

 to be altogether nothing but common salt. 



Thus if 100 drams of saltpetre is taken for assay the following 

 form may be observed. 



Drams. 



Taken for assay, saltpetre 100 



Recovered after washing and drying 79 



Impurities, 21 



^ Add one per cent, for mseluble matter sueh as gravel, 



sand, &c 1 



Total impurity 22 



Quality of the sample 78 per cent, purity. 



* The quantity of insoluble matter remaining in the sample, after the 

 assay has been completed will seldom exceed one per cent, but if necessary 

 it can be ascertained by dissolving what remains of the sample in boiling 

 water and passing the solution through filtering paper, the insoluble matter 

 will remain upon the paper, and can easily be collected, dried and weighedr 



