CHEMISTRY. 577 CHEMISTRY. rials is now guaianteeil by the sellers, and the jjoods inspected to sec that they meet the guaran- tee. Dairy products of various kinds have been subjected to systematic inspection, and of late this has been extended to materials used for in- secticides and funsicides, the consumption of which is assuming large proportions. The earliest treatise on methods of agricul- tural analvsis in the I'nited States was pub- lished by Prof. G. C. Caldwell in 18G9. Since 1SS4 the Association of Oincial Agricultural t hemists has been a potent factor in testing and developing methods of analysis. It holds an an- nual meeting and publishes a large volume of proceedings and pajicrs. Similar associations exist in Germany. Holland, and Belgium, and a number of other European countries. Feeding .xd JlET.Boi,isst Experiments. The analysis of plants as above shows the total amount of the constituents present: but as these are not all in form to be digested by the animal. digestion experiments are made by the chemist on live subjects. In these experiments the amount and composition of the feed consumed by the animal, and of the corresponding excreta voided, are definitely determined for a short period, and by calculation the percentages of protein, fat, fibre, and nitrogen-free extract ac. tually digested are ascertained. These percent- ages are called the coefficients of digestibility, and have to be determined for each feeding stuff separately. A method of artificial digestion has been worked out. in which the feed is treated with pepsin and hydrochloric acid and with pan- creas solution, but it is not generally considered to be as reliable as the natiiral method. In re- cent years the bomb calorimeter has come into (■(Uite extensive use in the study of feeding stuffs, for measuring the fuel value, or the capacity of the feed for furnishing heat and energy for work. In this apparatus a sample of the material is ignited with oxygen in a platinum-lined bomb, and the heat evolved is measured by means of very accurate thermometers, suspended in a water-jacket surrounding the bomb. For fur- ther details regarding fuel value and the sub- ject of animal nutrition in general, see Feeding Stitfs, and Feeding Farm Anim.ls. Very refined and delicate methods and appara- tus have also been elaborated for studying the functions of the different nutrients in animal feeding, and the way in which they are used in the animal body in producing animal heat and energy for work, repairing the waste of the body, and nuiking growth or meat or milk. In the ordinary feeding experiment with cattle, or sheep, or pigs, the herd is divided into equal lots, and fed in periods varying from a few weeks' to several months' duration, account be- ing kept of the amounts of food of known com- position which each lot or individual eats, and of the changes in weight. At the conclusion the animals are often slaughtered and the com- position of the carcass determined. In this way the feeding value of nearly every available feed- ing stuff, and of a great variety of compound rations, has been studied, and the specific effect of nutrients from different sources on the qual- ity of the beef, pork, butter, etc. Much of this feeding work has also been directed toward the relation of live stock to the problem of mainte- n.ance of soil fertility, anri the development of a rational system of agriculture. It has been shown that by feeding the crops largely on the farm where they are produced, and applying the ma- nure to the soil, the fertility of the latter can be conserved, the supply of humus kept up. and the expense for commercial fertilizers reduced to a minimum. The reason of this is that when crops are fed to growing stock or milch cows, from (10 to 90 per cent, of their fertilizing in- gredients, voided in the solid and liquid manure, are relaincil upon the farm. In studying the fundamental principles of nu- trition, and the function of the different nutri- ents, the total income and outgo of the body during the experimental period nnist be deter- mined. This includes the carbonic acid and other gases given off, as well as the excreta. For measuring these gases a respiration apparatus is employed, which usually consists of a closed chamber in which the animal or person is placed, with means for measuring and sampling auto- matically the air as it enters and leaves the chandler. With such a respiraticm apparatus Hennelierg, Kiihn, and others have worked out the functions and relative values of the different nutrients, and many of the underlying princi- ples of nutrition. Atwater and Itosa have com- bined a calorimeter with the respiration ajipa- ratus, and made many improvements in the accuracy of the latter. In their apparatus the chamber in which the subject is placed is a calorimeter, with very delicate arrangements for registering the heat given off by the subject. With the aid of this highly sensitive respiration calorimeter, it has been possible to demonstrate the absolute conservation of matter and energy in the body. A similar apparatus for use with animals has been constructed by Armsby. Fertilizer Experiments. The investigations of the agricultural chemist in studying the fer- tilizer requirements of different crops, the value of dilTerent forms of plant food and their effect on the quality of the crop, and a wide , lange of similar problems, are conducted either in pots or in plats in the field. The preliminary studies are often made in pots or boxes, filled with sterile sand, to which definite amounts of humus and fertilizers have been added. The conditions are under complete control, and every part of the plants can be saved for analysis. These pots are usually mounted on trucks, so that they can be placed under cover at night or during a rain. The plat work is especially for testing theories luider field coiuiitions. studying fertilizer requirements, the drauglit of different kinds of crops, the changes in humus content and fertility of the soil under various systems of trcatnicnt. and the like. The plats are most commonly about one-tenth of an acre in area, selected with much attention to uniformity of the soil, and often under-drained and provided with basins for collecting the drainage water from each plat. Great care is exercised in pre- paring the land, applying the fertilizers, culti- vating the crops, and harvesting them, so as to have the treatment of all uniform except as re- gards the special experimental feature. For studying soils in the field, samples are taken at intervals with a tube specially made for the pur- pose, which is driven into the ground to the depth required, removing a core of the soil. These sam- ples are taken to the laboratory and tested or analyzed. These studies of iilant production and soil fertility have been accompanied by a gradual
