SEWAGE SLUDGE.

142. Sludge from Sewage Disposal Plant, Stamford. Analysis:

Water 17.34 per cent, ash 38.95 per cent, organic and volatile matter 43.71 per cent, nitrogen 2.27 per cent.

21860. Activated sludge.

Sanitary District of Chicago. Manufacturer's sample. This is the product obtained in the process of purifying sewage by aeration methods.

Analysis:

Nitrogen in ammonia 0.06 per cent, organic nitrogen 5.42 per cent, total nitrogen 5.48 per cent, active insoluble organic nitrogen 2.93 per cent, inactive insoluble organic nitrogen 1.79 per cent, available phosphoric acid 3.00 per cent, total phosphoric acid 3.91, total potash 0.79 per cent.

The activity of the insoluble organic nitrogen is about 62 per cent by the method employed (alkaline permanganate).

LIME.

The application of lime for purposes of soil improvement has been practiced since very remote times. Marl and ash were used for this by the ancient Greeks and Romans and in early English history the practice of spreading chalk on the land is recorded. The early colonists in America brought the practice with them, and marl, ashes, and gypsum or land plaster are conspicuous in the records of colonial agriculture. With the advent of artificial fertilizers the use of liming materials was largely suspended but modern agricultural practice has restored lime to wider recognition than ever before.

In the earlier sense of the term "lime", a miscellaneous group of calcium-containing materials were included such as marls, chalk, oyster and clam shells, limestone, marble, and the ashes of wood and other organic substances in which calcium is combined wholly or in part as carbonate; gypsum or land plaster which is calcium sulphate; and phosphate of lime which is derived from phosphatic rocks and from bone. The current usage of the term, however, is more restricted and applies chiefly to calcitic and dolomitic limestones, oyster shell lime, calcareous marls and the several forms of lime derived from them.

The practical use of lime in New England may be discussed very briefly as follows:

1. The chief function of lime is to make the soil less "acid". The exact nature of this "acidity" is a matter on which scientists are not entirely agreed, but all agree that lime will change the reaction.

2. The soils of Connecticut are usually acid, due to lime deficiency of the rock from which they are derived, the relatively high leachiness of our soils, and the long period of time which

Also, due to

most of the tillable area has been under cultivation. the variable factors of original soil material, leachiness and past agricultural practice, our soils vary widely in the degree of acidity.

3. We are not so much concerned with soil acidity as such, as with the success of a large number of crops such as clover, alfalfa, timothy, redtop, tobacco, potatoes, tomatoes, lettuce, beets, carrots, spinach and many others. It has also been shown, particularly by the Rhode Island Station, that crops vary greatly in their sensitiveness to acidity and in their response to applications of lime. For instance, red top, strawberries and watermelons do very well under acid conditions while others, like beets, onions and alfalfa, require a condition much less acid. Certain diseases, like potato scab and tobacco root-rot, are controlled by keeping the soil moderately acid.

4. A knowledge of the intensity of soil acidity is manifestly of great importance as a guide to farm practice in regard to any given crop to be grown. The "litmus paper" test was formerly used in this connection, but it is not sufficiently sensitive to show the finer distinctions in soil reaction that modern research has shown to be necessary, and there are much better methods, which, while far more perfect, do give a fairly accurate estimate of the degree and intensity of the acidity.

Our liming practice should therefore be based on the following information:

a- What crops are to be grown?

b- What amounts of stable manure are used?

C- What kinds and amounts of fertilizer are used?

d- When, in what form and what amounts has lime been used?

e- What is the reaction of the soil?

This last can be learned by sending representative samples from various fields to the Experiment Station. Such samples should be accompanied by the information indicated in a, b, c and d above, if advice is desired relative to the use of lime.

The inference should not be drawn that we now have accurate information on all the problems concerned with "acidity," but progress is being made and on certain crops there is quite accurate information.

The relation between actual lime (calcium oxide, CaO), and the several natural and manufactured lime products is illustrated as follows: If 100 lbs. of pure crushed limestone are burned in a kiln at suitable temperature (650-900 °C. or 1200-1650 °F.), 56 pounds of actual lime (calcium oxide, CaO), are obtained, the remaining 44 pounds being lost in the form of carbon dioxide gas (CO2). This actual lime is known also by other names such as "stone lime" or "quicklime". Actual lime or quicklime is very

irritating to handle and in practice slaked lime is more often used. This is obtained by treating quicklime with water, with which it combines vigorously with the production of considerable heat. There is enough moisture in the air to accomplish the slaking process, but a longer time is required. The 56 lbs. of actual lime obtained from the original 100 lbs. of limestone will obviously increase in weight as it combines with water and will weigh 74 lbs. when completely slaked. This slaked lime is otherwise known as hydrated lime, calcium hydrate or calcium hydroxide. When quicklime is allowed to air-slake, however, it absorbs carbonic acid as well as moisture from the air so that the product is a mixture containing some quicklime, hydrated lime and carbonate of lime, or, in other terms, calcium oxide, calcium hydrate and calcium carbonate.

The changes described take place also in the case of limestones which contain magnesium (dolomitic limestones), the product of burning being in such cases the mixed oxides of lime and magnesia.

Commercial liming materials are judged on the basis of actual lime and magnesia (oxides of calcium and magnesium), which they contain, and upon their degree of fineness. The various products are quite variable in composition but in general they will contain mixed oxides about as follows:

bonates....

.45-55

..40-50

.40-50

.65-75

Hydrated lime, high grade, less than 10% car

Low grade, mixture of hydrate and carbonate....55-65
Lime ashes...

...50-60

The effectiveness of lime in the soil will depend directly upon its degree of fineness. Neither the carbonates nor hydrated limes are readily soluble in soil water and the rate at which they will be dissolved will depend upon the size of the particles. The smaller the grains the greater the relative amount of surface exposed to the action of the solvent.

FINENESS OF LIME.

Since there is a direct relationship between the fineness of lime products and their rate of availability in the soil, it might appear that the greatest degree of fineness is desirable. Yet because of the cost of grinding the lime to a very fine condition and the rapidity with which such material disappears in the soil, a medium ground lime seems to be the more desirable commercial product. A reliable authority assumes that pulverized limestone, all of which will pass a 10 mesh sieve, 70% of which will pass a 50 mesh

sieve, and 50% of which will pass a 100 mesh sieve, should give excellent results and yet be cheap enough to make its use worth while. In Ohio the standard required by law for agricultural ground limestone is that 95% of the material shall pass a 10 mesh screen, 50% shall pass a 50 mesh screen, and 30% shall pass a 100 mesh screen.

If immediate effects are desired in the use of moderate quantities of lime for a special crop of high money value, extreme fineness may be desirable, regardless of the greatly increased cost. This is usually obtained in hydrated limes.

In table XX are given analyses of 46 samples of lime. Some of these were collected and examined two years ago but the results have not been published.

COMMENTS ON ANALYSES.

22349. This was a sample of limestone dust which accumulated in the manufacture of poultry grit and was not offered for sale as an agricultural lime.

23030, 23031, 23254. The first two samples were submitted by purchasers. The manufacturer advised that the analysis of 23030 was quite unlike the composition of their product as shown by frequent check analyses of their own. Accordingly an official sample, 23254, was drawn which was supposed to be the same material as 23030 but was sampled from different stock. This showed a composition substantially in accord with the manufacturer's claim and in agreement also with purchaser's sample. 23031. Evidently 23030 had become mixed with some material containing a relatively large amount of insoluble matter.

The cost of lime, so far as ton prices have been quoted to us, show considerable variation. Thus, four quotations for limestone have varied from $6.75 to $10.00 per ton. For hydrated lime, containing from 62 to 77 per cent of effective oxides, prices have ranged from $9.50 to $15.00.