a04 WATER HYGIENE 
finally in the hot-water oven until all the moisture has disappeared. 
Grind the dry material to a fine powder and keep it in a glass-stoppered 
bottle. 
Reagents. 1. Sulphuric acid. Concentrated, nitrogen free. 
2. Copper sulphate solution. Ten per cent. 
3. Potassium permanganate. Crystals. 
Procedure. Weigh accurately 0.5 gm. of dried sludge or 5.0 gms of 
dried mud and put it in a 500 ¢.c. Kjeldahl flask. Digest it with 20 c.c. 
of sulphuric acid, or morc if necessary, and 1 c.c. of copper sulphate 
solution to assist the oxidation. Boil for several hours until the liquid 
becomes colorless or slightly yellow. Oxidize the residue with 0.5 gm. 
of potassium permanganate, and follow the “ Procedure for Sewage ” 
(p. 165). 
The following method is convenient for routine work at sewage 
disposal plants. Digest 0.5 gm. of dried sludge or 5.0 gms. of dried mud 
with 20 c.c. of strong sulphuric acid and 1 c.c. of the copper sulphate 
solution in a 300 c.c. Kjeldahl flask. After digestion for several hours, 
cool, transfer to a glass-stoppered 100 c.c. flask, dilute with distilled 
water to 100 c.c., and mix well. Transfer 50 c.c. with a pipette into 
another 100 c.c. volumetric flask, and make this portion alkaline with 
50 per cent sodium hydroxide, testing a drop of the liquid on a porcelain 
plate with phenolphthalein to insure neutralization. The formation of 
a, floc usually indicates that the neutralization is complete. Pour the 
solution into a small glass-stoppered bottle and permit it to stand until 
the next day. Nesslerize an aliquot portion of the clear, supernatant 
liquid, and calculate the percentage of nitrogen in the material. 
Fats. Fats are usually determined only on sewage sludge, but some 
mud deposits contain small quantities due to the presence of trade 
wastes. ; 
Procedure. Weigh, according to the quality of the sewage or mud, 
0.5 to 25 gms. of dry material. Add water to the weighed portion in a 
porcelain dish and acidify the mixture with N/50 sulphuric acid in the 
presence of litmus tincture or azolitmin solution indicator. Avoid 
adding too much acid as an excess gives too high results on account of 
fatty acid residues. Evaporate the acidified mixtures to dryness on 
the water bath, and heat it in the hot-air oven at 100° C. for two to three 
hours. Extract the dry residue with boiling ether, rubbing the sides 
and bottom of the dish to insure complete solution of the fat. Three 
extractions with ether are usually sufficient. Filter the ether solution 
through a 5 cm. filter paper into a small flask. Evaporate the ether 
slowly, dry the fatty extract for half an hour at 100° C., cool in a des- 
