after two or three hours, and when the weight is constant, the 

 filter-paper is brought out of the tube, fitted on to a funnel, 

 wetted, and the solution of the Nitrate to be analysed passed 

 through into a clean beaker. The residue on the filter- 

 paper is thoroughly washed, covered up with a clean piece of 

 paper, and the funnel left in the water-oven to dry. Next day, 

 the filter-paper is taken out with the insoluble residue on it, 

 put inside the tube again, left in the water-oven, after an 

 hour taken out, stoppered, and after a few hours weighed. 

 It is weighed again after a few more hours until the weight 

 is found to remain constant. The difference of weight gives 

 the amount of insoluble matter in 35 grams of the Nitrate 

 analysed. This is therefore 



(1) The total insoluble matter > including sand. The filter- 

 paper is ignited white, and put in a weighed platinum cruci- 

 ble. The increase of weight is due to sand and other 

 siliceous matter alone, the usual allowance being made for the 

 filter-paper ash. 



(2) The moisture is determined in the usual way. 3 

 grammes are weighed out in a watch glass, left in the water- 

 oven, weighed next day, and weighed again, both times 

 when cool, until the weight is constant. The loss of weight 

 is due to the amount of moisture in the 3 grams of the 

 sample of the Nitrate. 



: (3) Sodium Chloride. The filtrate containing the re- 

 mainder of the 35 grams, after the insoluble matter has been 

 separated, is made exactly into half a litre or 500 c. c. Of 

 this, should be sucked out joo c. c. containing 7 grams of 

 the Nitrate analysed, by means of a large pipette, and 

 placed on a clean porcelain bason. This is treated with 2 

 drops of K 2 CrO 4 which is used as an indicator. The standard 

 solution of Silver Nitrate is taken in a burette. When the 

 surface of the solution inside the burette stands exactly at 

 p c. c. it is gradually poured on the Nitrate-solution by 

 using the clip. The mixture on the. bason is kept con- 



