has been given off, in order to disengage the albuminoid ammonia. This measure should have a firm bottom, and pour steadily.

A 100 c.c. measuring flask is required for measuring the quantity of effluent wanted for distillation, a 25 c.c. flask for the quantity of sewage taken for this purpose, and a 500 c.c. flask for measuring the distilled water.

By always taking the same quantity in the same flask for the various processes, the method of analysis becomes automatic, and accuracy is ensured.

FIG. 9.-METAL BURETTE-STAND
AND BURETTE.

Burettes and a Burette-stand.

Burettes, to contain standard nitrate of silver for estimating the chlorine and another for the oxygen consumed, are also necessary. When a burette has been finished with, the remaining standard solution may be run off into the stock-bottle. The burette should then be drained dry, plugged with cotton-wool to keep out dust, inverted on the burette-stand, and kept in this position with the tap open. Before use a small quantity of the standard solution should be run through the tap, and before each estimation the burette should be filled, so that the bottom of the curved surface of the standard solution stands accurately at 0.

A metal burette-stand is recommended, as it is firmer than a wooden one (see Fig. 9).

A smaller burette may also be required for containing deci-normal hydrochloric or sulphuric acid, or decinormal sodium carbonate, for estimating the alkalinity or acidity of the sewage.

A 200 c.c. porcelain dish is required for the estimation (by the nitrate of silver solution) of the chlorine as chlorides.

Pipettes.

A 5 c.c. graduated pipette for measuring the standard solution of ammonia is used, and should be kept as far as possible for this use.

Pipettes to deliver 10 c.c. are used to measure the quantity of effluent required for the estimation of nitrates, and also for measuring the solutions in the oxygen-absorption process, and in the former process a 1 c.c. pipette to deliver 1 c.c. is also used to measure the phenol-sulphuric acid.

Other Apparatus.

11. For the estimation of the nitrogen as nitrates, three small 25 c.c. beakers are necessary for evaporating to dryness on the waterbath the 10 c.c. of water used in

this process. The beakers should be scratched 1, 2, and 3 with a diamond, or be marked

with a file, so that no mistake can arise when two beakers and a standard are being evaporated to dryness at the same time.

In addition to the above appliances, the following apparatus is also necessary :

Two funnels-a large (6-inch) funnel for filling the distillation flask for the ammonia process, and a small (3-inch) funnel for making the standard solutions.

Several watch-glasses-large and small.

Two or more of Fletcher's safety Bunsen burners.

One or more iron tripods.

A pair of crucible tongs.

A packet of 3-inch Swedish filter

papers.

Several lengths of glass tubing.
A few pieces of glass rod.

Several 4-ounce stoppered bottles for incubating 100 c.c. of the effluent for the incubator test.

An incubator is also necessary for this test; either Hearson's or a cheaper one, as shown in Fig. 10, will do.

CHAPTER II.

STANDARD SOLUTIONS USED IN AND METHODS OF

SEWAGE ANALYSIS.

12. All the standard solutions required may be purchased ready for use from the leading chemists. Of course it is desirable to know how to make these solutions, and with the apparatus described in the previous chapter they may be prepared quite accurately. Ammonia-free water is an essential for this purpose. If a good public water-supply which easily yields ammonia-free water is not obtainable, it will be necessary to purchase ammonia-free water, and this should always be at once tested with Nessler's test (sec. 19 b). If it gives the slightest discoloration it should be returned.

It should be clearly understood that every dish, tube, and flask must be absolutely clean before use. This is a simple matter when there is a good public water-supply; where, however, the public supply is of indifferent quality, it will be necessary to rinse everything out with distilled water after it has been washed with tap

water.

The sewage for analysis should be collected in a glass-stoppered bottle; a Corbyn quart is sufficient. The date of collection and particulars of the rainfall should be noted at the time.

The results of analysis are most easily expressed in parts per 100,000, but as there are 70,000 grains to the gallon, the results may afterwards be expressed as grains per gallon by decreasing them in the proportion of 10 to 7-that is to say, by dividing by 10 and multiplying by 7. See Table IV., p. 215.

When all particulars are required, the order of work in the analysis of the sewage should be somewhat as follows:

First enter particulars of source of sewage, etc., in the analysisbook, noting the appearance of the sample, the amount of suspended matter, and any smell. The sample should be shaken up, the result of the shake test noted, and the depth of the colour required to obliterate Pearl type (see p. 18). It must be clearly understood that the sample should be analyzed as soon as practicable after collection, and the actual analysis should then take place in the following order, so as to take up a minimum amount of time :—

i. For the Total Solids.-If required, start 100 c.c. to evaporate down to dryness on the water-bath.

ii. For the Free and Albuminoid Ammonia.-Start the distillation of 25 c.c. of a sewage or 100 c.c. of a sewage effluent in 500 c.c. of distilled water.

iii. For the Estimation of Nitrates.-Set 10 c.c. of the effluent and 10 c.c. of the standard nitrate solution to evaporate nearly to dryness by placing the two beakers on the top of the water-bath.

iv. Estimate the Chlorine as chlorides in 100 c.c. of the sewage. v. Finish the Estimation of the Free and Albuminoid Ammonia. vi. Finish the Estimation of the Nitrates.

vii. Estimate the Oxygen absorbed in three minutes, and fill a 4 oz. bottle full of the sample in the incubator to incubate for one week at 80° F.

viii. Estimate the Alkalinity with Methyl Orange and Decinormal Sulphuric Acid.

Total Solids.

13. Having thoroughly cleansed, dried, and made a note of the tare weight of the nickel dish as described (sec. 3), put it on the water-bath and light the gas. Shake the sample of sewage up and measure 100 c.c. in the measuring-flask; pour this carefully into the nickel dish, and leave it on the water-bath until dry; then remove it with a pair of crucible tongs, wipe the outside of the dish so that no dirt from the water-bath adheres to it, transfer it to the steamoven and leave it for half an hour. It must then be set aside to cool in the desiccator. The dish and its contents must be weighed as rapidly as possible.

Ordinary sewage will contain about 140 parts per 100,000-that is, will contain about 0.14 gramme in the 100 c.c.

The gross weight should then be entered in the weighing-book, with the number of the sample, over the top of the tare weight of the dish, which is then to be subtracted thus:

1899. MARCH 25TH. SAMPLE No. 250, AVERAGE SEWAGE.

Residue from 100 c.c. of sewage taken and dish weigh
Tare weight of dish ...

That is to say, the sewage contains-

0.14 gramme in

1.4 gramme in

100 c.c., or 1,000 c.c., or

140 grammes in 10,000 c.c., or 1400 grammes in 100,000 c.c.

That is, 140 parts of solid matter in the 100,000.

It

It is not necessary to write every calculation out in this way. will be sufficient to remember that when 100 c.c. of sewage are taken the number of milligrammes gives the parts per 100,000. If the result be wanted in grains per gallon, multiply the result obtained by 7 and divide by 10, or see Table IV., p. 215.

If it be required to know the solids in suspension, first estimate

* This is practically prevented by using a porcelain ring on the water-bath.

the solids in 200 c.c. of the sewage, by adding 100 c.c. to the dish in which the first 100 c.c. have been evaporated down; the weight given by the 200 c.c. should be double that of the 100. Then filter the sewage through filter-paper, and estimate the solids in 200 c.c. of the filtrate. The difference between the two weights will be due to the weight of the suspended solids in 200 c.c. of the sewage.

14. Estimation of the Free and Albuminoid Ammonia.

(a) Standard Solution of Ammonia.-Dissolve 3.150 grammes of ammonium chloride in 1 litre of water. Label: STRONG AMMONIUM CHLORIDE SOLUTION.

Pipette of 5 c.c. of this strong solution (when it is completely dissolved and properly mixed) into the 500 c.c. measuring flask, and make up to 500 c.c. with ammonia-free water. Label: STANDARD AMMONIA SOLUTION (1 c.c. = 0·00001 gramme of Ammonia).

(b) Nessler's Solution.-Dissolve 62.5 grammes of iodide of potash in 235 c.c. of distilled water; put 1 c.c. of this solution aside. Make a cold saturated solution of corrosive sublimate by dissolving 35 grammes of powdered perchloride of mercury in 600 c.c. of warm distilled water. When this is cold add it gradually to the iodide solution until a slight precipitate appears. The precipitate should then be redissolved by adding as little as possible of the 1 c.c. of iodide of potash solution set aside. Add 150 grammes (5.29 oz.) of caustic potash dissolved in 150 c.c. of water. This will make about a litre of Nessler's test. Set aside in a bottle fitted with a rubber bung, and decant off the clear portion for use. Label: NESSLER'S SOLUTION.

(c) Alkaline Permanganate Solution for Albuminoid Ammonia.— Dissolve in the large porcelain dish 7 ounces of caustic potash sticks in 1,100 c.c. of ammonia-free distilled water; add 8 grammes of pure permanganate of potash and boil down to 1,000 c.c. If 50 c.c. distilled with 250 c.c. of ammonia-free water yield no ammonia, the solution is accurately prepared. If it yields ammonia it requires further boiling to drive off the ammonia. Care should be exercised that no dirt falls into the dish. The best way to measure the 7 ounces is to counterpoise the big dish on a good pair of scales, and then take out the sticks of potash with a clean pair of forceps which have been heated in a Bunsen burner, transferring the sticks of potash to the dish until 7 ounces is turned. Label: ALKALINE PERMANGANATE SOLUTION.*

Having cleansed the distillation-flask with a little hydrochloric acid, it should be well rinsed out to get rid of all acid. Measure out 25 c.c. of the sewage with a pipette or 100 c.c. of the effluent with a measuring-glass, and pour carefully through the larger funnel into the

*The caustic potash is sold in 1-pound bottles. The remaining 9 ounces should be at once transferred to a large, wide-mouthed glass-stoppered bottle, as it does not keep in the corked bottles after they have once been opened.