distillation-flask, and make up to 500 c.c. with ammonia-free distilled water. Wash the thistle funnel and tin pipe by passing clean water through them, or by letting the tap-water flow through. Then clean the tin pipe of the condenser in a similar way. The distillation-flask is then to have its bung, which should be rinsed clean, inserted into it; then its tin pipe is to be fitted into the block-tin pipe of the condenser, and the flask is to be clamped into position, the condenser being fixed at such a height that the lower end of it permits the Nessler glasses in their stand going under it. If the sewage is acid, it should be rendered alkaline by a little freshly burnt carbonate of soda crystals dissolved in ammonia-free water. All now being ready, the water is turned on through the condenser, the Nessler tube marked 1 brought under the block-tin pipe of the condenser, and the lighted safety Bunsen burner brought direct under the flask. To prevent the flask breaking, two precautions must be taken: first, the outside is to be wiped dry before applying the naked flame; second, the flame must never be allowed to play upon any part of the flask above the level of the water, therefore at the end of the process, when there are only about 100 c.c. left in the flask, the flame must be lowered. As soon as tube No. 1 is full up to the 100 c.c. mark, the stand should be moved along for the condenser to deliver into tube 2. As soon as this is full, 2 c.c. of Nessler's solution should be dropped into it and the stand moved on to the blank tube. If tube No. 2 gives no yellow tint, all the free ammonia has come off in the first tube, and the 50 c.c. alkaline permanganate may be poured in. If tube 2 shows a trace of ammonia, the blank tube must be allowed to collect about 50 c.c. more, that is, to be half filled, and to this 2 c.c. of Nessler's test are to be added. If the test shows that ammonia is still being given off, this must be poured into a flask, and more collected, until all the ammonia has come off. As soon as no colour is given with the Nessler test, 50 c.c. of the alkaline permanganate are to be measured in the clean measuring glass, and poured gently through the thistle funnel into the distillation flask, tube No. 3 having been previously placed under the condenser to collect the albuminoid ammonia. As soon as tube 3 is full, tube 4 is to be brought under, and as soon as this is half full it is to be Nesslerized. If it contain no ammonia, as shown by there being no colour on the addition of the Nessler's test, the gas may be turned off, as the process is complete; if it does contain ammonia, more distillate is to be collected in the spare tube, the contents of which, if they contain any free ammonia, are to be first transferred to a flask for estimation afterwards. As a rule, working with the quantities suggested, all the free ammonia comes off in the first 200 c.c. if the sewage is rendered alkaline by carbonate of soda, and all the albuminoid ammonia in the first 150 c.c., after the alkaline permanganate has been added. If more than 250 are distilled off for the free ammonia and more than 200 for the albuminoid ammonia, the flame must be lowered so that it does not play upon the glass above the water level, and, if necessary, 50 or 100 c.c. of ammonia-free water should be poured through the thistle funnel so that the distillation may be continued further. As a rule, there is no necessity for collecting and estimating the free ammonia. 200 c.c. may be distilled over into a 200 c.c. flask, put aside, and a 50 c.c. glass put under the pipe. When full it is tested with Nessler, and if a reaction is got it is thrown away and another 50 c.c. collected, which is tested in a similar manner. If there is no reaction with Nessler's reagent, then the alkaline permanganate is added to the Florence flask, and the albuminoid ammonia collected in 2 one-hundred Nessler glasses and subsequently estimated. When the free and albuminoid ammonia are all off, each tube has to be Nesslerized, and the depth of colour has to be matched with standard ammonia. This is done in the following manner: 2 c.c. of Nessler's test are dropped into each tube, which should be allowed to stand for two minutes. With a little experience an approximate idea will be obtained as to the probable amount of standard ammonia solution required to match the depth of colour. Suppose it is decided to try 5 c.c., this quantity of the weak standard ammonia solution is pipetted into the graduated Nessler glass; this is then diluted with ammonia-free distilled water up to about 90 c.c., then 2 c.c. of Nessler are added, and it is made up to the 100 c.c. mark with ammonia-free distilled water; this tube, which we shall call the "standard 5," is then left for two minutes. 80 100 If tube 1 is lighter, the standard solution should be poured into the graduated cylinder (sec. 11) until the shades match, and the quantity of the standard left is to be read off. If 80 c.c. of the 100 c.c. are required to match the tint, tube 1 is equal to of standard 5 c.c.-that is, standard 4 c.c. and tube No. 1 will contain 0.00004 gramme of ammonia; then tube 2 must be estimated in the same manner. If the tube 1 is darker than standard 5, it should be diluted with tube 2 and the two tubes then be estimated. If they are still too dark, as is usually the case with sewage, they can be poured into a 200 c.c. flask and thoroughly mixed, and the quantity is measured, which gives the same shade as the standard 5, from which the whole of the free ammonia in the 200 c.c. can be estimated. Thus, suppose 20 c.c. of the 200 c.c. equal the standard 5, a simple proportion sum shows the whole to equal a standard 50. The first thing, therefore, is to ascertain what amount of standard solution the free ammonia is equal to call this x; then, knowing that 1 c.c. of standard solution equals 0.00001 gramme of ammonia, the free ammonia in the 25 c.c. sewage equals 0'00001 multiplied by a grammes. To save time, the following table can be used, giving the ammonia in parts per 100,000 for each c.c. of standard solution used, when 100 c.c., or 25 c.c. of the effluent or sewage are taken for analysis : : TABLE I. GIVING THE AMMONIA IN PARTS PER 100,000 FOR EACH C.C. OF STANDARD The author has worked with as small a quantity as 25 c.c. of sewage now for some years, and has found that perfectly accurate results can be obtained if the water added is absolutely free from ammonia, and thorough mixing of the distilled water and the distillate is made a point of, before Nesslerizing. 15. Estimation of the Chlorine. Standard Solutions. (a) Nitrate of Silver.-Dissolve 4.79 grammes of nitrate of silver in 1000 c.c. of distilled water. Label: STANDARD NITRATE OF SILVER SOLUTION (1 c.c. = 0·001 gramme of chlorine. c.c. of water, each c.c. 1 part per 100,000). With 100 (b) Indicator of Potassium Monochromate.-Dissolve 1 part of the pure salt in 10 of water, and keep in a drop bottle. The chlorides are estimated as chlorine in the following manner : The 100 c.c. measuring-flask is filled up to the mark with the sewage or effluent to be examined; this is then decanted into the 200 c.c. porcelain dish, and two drops of the 10 per cent. monochromate of potash solution are added so as to give the sewage in the dish a canary-yellow colour. The nitrate of silver burette is then to be filled to the 0 mark with the standard nitrate of silver solution, 1 c.c. of which precipitates 0.001 gramme of chlorine. The standard nitrate of silver solution is then carefully run into the dish, which is stirred with a clean glass rod until all the chlorine is precipitated. This is known by the nitrate of silver then forming the red chromate of silver with the chromate of potash. As soon as there is the slightest red tinge, which does not disappear on stirring, the amount of standard nitrate of silver used should be read off. The result is the number of milligrammes (0·001 gramme) in 100 c.c., and therefore the number of parts per 100,000. The reaction is a very delicate one, and at the end the nitrate of silver should be addedc.c. at a time. With sewages it is, as a rule, necessary to filter before making the estimation. 16. Nitrogen as Nitrates and Nitrites. (a) Standard Potassium Nitrate Solution.-Dissolve 0.072 gramme of recently fused potassium nitrate in 1,000 c.c. of water. Label: STANDARD NITRATE SOLUTION (10 c.c.=0.0001 gramme of nitrogen). (b) Phenol Sulphuric Acid.-Add 6 grammes of pure phenol and 3 c.c. of distilled water to 37 c.c. of pure sulphuric acid free from nitrates, and digest for eight hours at about 180° F. This reagent can be purchased ready for use. (c) Liquor Potassa.-Make a 5 per cent. solution of caustic potash (free from nitrates) in distilled water, or use liquor potassæ B.P. Measure 10 c.c. of the water to be examined in a 10 c.c. pipette, and run it out into a small beaker. Wash the pipette through with distilled water, and then measure 10 c.c. of the nitrate of potash solution into another small beaker, making a written note of the number of the beaker in which each is contained. Place the two beakers on the upper part of the water-bath at the same time as the total solids are being evaporated down. Take them off as soon as they are dry, or there may be loss of nitrate of ammonia. When they are both cold, add to each 1 c.c. (measured in a 1 c.c. pipette) of phenol sulphuric acid. Put them again on the water-bath for ten minutes. Then wash each beaker out carefully into a Nessler tube, using successive quantities of water, until each tube is half full; then add to each 25 c.c. of liquor potassæ, and fill up each tube to the 100 c.c. mark. Any nitrates present convert the phenol sulphuric acid into picric acid, which by the action of the caustic potash forms picrate of potash, the intensity of the colour depending upon the amount of nitrates present. The standard is equal to 1 part per 100,000. If the Nessler glass containing the effluent being examined is darker, measure in a 100 c.c. measuring-glass, graduated in c.c.'s, the quantity equal to the standard tube; if 80 is equal to it, then the quantity present is as follows: 80: 100::1:x= 1.25, the nitrogen as nitrates being 1.25 parts per 100,000. If the tube is lighter than the standard, pour off the standard until the tint is matched; then if 75 c.c. are left in the standard tube, the nitrogen as nitrates is 75 part per 100,000. The following table will be found useful for rapidly ascertaining the quantity of nitrates present: TABLE II. GIVING PARTS PER 100,000 OF NITROGEN AS NITRATES FOR EACH C.C. OF |