WATER ANALYSIS 23 



iooo c.c. of water sample ; (3) Reduce bulk by moderate 

 heat, avoiding boiling or spurting. Or, to a small dish 

 successive quantities of the sample are added, a note being 

 kept of the amount ; (4) Evaporate to complete dryness 

 at ioo C. (212 F.) on water-bath ; (5) Now place in 

 water-oven at ioo C. for half an hour to remove all traces 

 of moisture. Some analysts advise this drying to be done 

 at 105 C. in hot-air chamber ; (6) Cool in dessicator ; 

 (7) Weigh. To make quite sure that residue is dry, items 

 5, 6, and 7 can be repeated until weight is constant ; (8) 

 Subtract weight of dish ; difference is weight of total 

 residue in amount of sample taken ; (9) Calculate as 

 parts per 100,000, and as grains per gallon. 



Fixed Solids. (1) Incinerate the dried solids at as low 

 a heat as possible ; (2) Watch the process for blackening 

 or charring, fumes or odour. A piece of dry starch and KI 

 paper held over crucible will detect any nitric oxide given 

 off ; (3) Cool and weigh ; (4) Difference from weight of 

 dish gives fixed solids in amount of sample taken. Calcu- 

 late as before. 



Volatile Solids. Total solids less fixed solids, gives 

 volatile. Consist of organic matter, nitrates, nitrites, 

 ammoniacal salts, combined water, combined carbonic 

 acid, and sometimes chlorides. Should not exceed 1-5 

 per 100,000 in a very good water. 



Example. Evaporated 200 c.c. sample water to dryness, 

 dried in air-oven, cooled in dessicator, and weighed : 



Weight . . . . . . 19-674 grammes. 



Weight of platinum dish.. 19*554 ,, 

 Difference . . . . . . 0-120 gramme. 



i.e., 0-120 grm. in 200 c.c. water, or 0-060 grm. in 100 c.c. 

 or 100 grm., or 60 grm. in 100,000 grm., or 60 parts per 

 100,000 parts. 



Incinerated total residue at low heat. No blackening, 

 fumes, odour, nor change in starch and KI paper. Cooled 

 and weighed : 



Weight . . . . . . 19-650 grammes. 



Weight of platinum dish . . 19-554 

 Difference . . . . . . 0-096 gramme. 



