In the analysis of a sample of green vitriol it will be sufficient to determine the moisture, water of crystallization, iron, and sulfuric acid. The moisture may be ascertained by drying the finely powdered sample over sulfuric acid for a few hours. The water of crystallization is separated by exposing the sample to a temperature of 285° for two hours. The iron may be determined by oxidizing to the ferrous state by boiling with nitric acid and then precipitating with ammonia, and proceeding as directed for iron analysis. The sulfuric acid is separated as barium sulfate and determined as already directed.
289. Stall Manures.—There are no definite methods to be described for the analyses of that large class of valuable fertilizer produced in the stable and pen, and which collectively may be called stall manures. The methods of sampling have already been described,[245] but only patience and tact will enable the collector to get a fair representation of the whole mass. These manures are a mixture of urine, excrement, waste fragments of fodder, and the bedding used for the animals. With them may also be included the night soil and waste from human habitations and the garbage from cities. All of these bodies contain valuable plant foods and the phosphoric acid, potash, and nitrogen therein are to be determined by the methods already given for these bodies when they occur in, or are mixed with, organic matter. In general, stall manures are found to have a higher manurial value than is indicated by the amount of phosphorus, potash, and nitrogen which they contain. Through them there is introduced into the soil large quantities of humus bodies whereby the physical state of the soil is profoundly modified and its adaptability to the growth of crops, as a rule increased. The addition of active nitrifying ferments in stall manure is also advantageous. Stall manures, however, may in many cases prove to be injurious to a crop, as for instance, when they are applied in a poorly decomposed state and in a season deficient in moisture.
It is essential therefore that the bedding of animals be in a finely divided state, whereby not only are the absorptive powers of the organic matter increased but also the conditions for their speedy decay favored. To avoid the loss of ammonia arising from decomposing urine it is advisable to compost the stall manure with gypsum or to sprinkle it from time to time with oil of vitriol.
In the analysis the moisture may be estimated by drying a weighed portion of the sample to constant weight at 100° or at a lower temperature in a vacuum. The potash and phosphoric acid are determined as usual, with previous careful incineration, and the nitrogen secured by the moist combustion process.
290. Hen Manure.—This fertilizing substance is a mixture of the excrement of the fowl yard with feathers, dust, and other débris. Measured by the standard applied to commercial fertilizers hen manure has a low value. As in the case of other farm manures, however, it produces effects quite out of proportion to the amount of ordinary plant foods which it contains. In a sample examined at the Connecticut station the percentages of fertilizing constituents were found to be the following[246]:
| Water | 51.84 |
| Organic and volatile matters | 24.27 |
| Ash | 23.89 |
The organic matter contained 0.61 per cent of nitrogen as ammonia and the ash 0.97 per cent of phosphoric acid, and 0.59 per cent of potash, all calculated to the original weight of the sample. The percentage of water in this sample is undoubtedly higher than the average, so that it can hardly be taken to represent the true composition of this manure. The potash, phosphoric acid, and nitrogen are to be determined by some one of the standard methods already described, the two former after careful incineration.
291. Guanos and Cave Deposits.—The principal constituents of value in these deposits are nitrogen and phosphoric acid. The other organic matters are also of some value but have no commercial rating. The nitrogen may be present in all its forms; viz., organic, ammoniacal, amid, and nitric, and for this reason is well suited not only to supply nourishment to the plant in the earlier stages of its growth but also to cater to its later wants. In guano deposits in caves, due usually to the presence of bats, similar forms of fertilizers are found and the soluble constituents due to decay and nitrification are protected from the leaching to which they would be subjected in the open air.
In many localities in the United States these deposits are found, but the humidity of our climate has prevented the immense open deposits of guano that characterize some of the arid islands of the Pacific Ocean.
Many bat guanos examined in this laboratory have also been found to contain potash, in one case 1.78 per cent. It is suggested therefore that the analyst do not omit to examine each sample qualitatively for this substance and to determine its amount when indications point to its presence in weighable proportions. In the many samples of bat guano of American origin which have been analyzed in this laboratory in the last few years some very rich in plant food have been found. In one instance the total percentage of nitrogen present, was 10.11 per cent. In some cases the phosphoric acid is high but rarely in conjunction with a high content of nitrogen. In one instance where the total phosphoric acid reached 14.53 per cent, the content of nitrogen was 4.87 per cent.