One liter of the above solution is enough for ten samples, each of 100 cubic centimeters. This quantity is placed in an erlenmeyer, which is stoppered with cotton and sterilized by being kept at 100° for an hour on three successive days. The erlenmeyer should be sterilized beforehand by heating for an hour at 150°. The freshly precipitated and washed calcium carbonate should be sterilized separately and added to each erlenmeyer at the time of seeding. Enough should always be used to be in excess of the nitrous and nitric acids found. The seeding is accomplished by filling a sterilized spoon which holds approximately half a gram of the soil, from the contents of one of the brass tubes, lifting the plug in the erlenmeyer and transferring quickly to the flask. This should be done in a perfectly still room, preferably as high above the ground as possible and in a place free from dust and under cover. The cotton plug being replaced the erlenmeyer is shaken until the sample of soil added is thoroughly disintegrated and intimately mixed with its contents. With care and experience the seeding is easily accomplished without danger of accidental contamination. At the end of each period of five days the beginning and progress of nitrification should be determined by some of the methods described in volume first. Either the ammonia can be determined by nesslerizing or the nitrous and nitric acids estimated. For nitrous acid we prefer the method described in volume first, paragraph =504=, and for nitric the one in same volume paragraphs =497= and =498=. By supplementing the analysis of a soil by the above described experiments in nitrification the analyst will be able to judge with sufficient accuracy of its needs for nitric nitrogen. =222. Quantity of Chile Saltpeter to be Applied.=—The quantities of Chile saltpeter which should be applied per acre vary with so many conditions as to make any definite statement impossible. On account of the great solubility of this salt no more should be used than is necessary for the nutrition of the crop. For each 100 pounds used, from fourteen to fifteen pounds of nitrogen will be added to the soil. Field crops, as a rule, will require less of the salt than garden crops. There is an economic limit to the application which should not be passed. As a rule 250 pounds per acre will prove to be a maximum dressing. The character of the crop must also be considered. Different amounts are required for sugar beets, tobacco, wheat, and other standard crops. It is rarely the case that a crop demands a dressing of Chile saltpeter alone. It will give the best effects, as a rule, when applied with phosphoric acid or potash. But this is a branch of the subject which cannot be entered into at greater length in this manual. The reader is referred to Stutzer’s work on Chile saltpeter for further information.[183]