Page:The New International Encyclopædia 1st ed. v. 04.djvu/658

* CHEMISTRY. 576 CHEMISTRY. In the analysis of the ])hint, we fiml first that the tissue contains a very large pLMcentage of water — up to 00 per cent. — which is indispen- sable to its growth and circulatory system. This water is expelled by licating the plant in a dry oven at about 212° F. for several hours. The residue, or ilr/i matter, consists of organic con- stituents and a relatively small proportion of ash. The former are <'ombustible. anil lience the asli is determined by burning the sample. The ash, consists chiefly of lime, magnesia, potash, soda, iron, silica, chlorine, and carbonic, sulphuric. and phosphoric acids. In plant analysis, deter- minations are made of all these const itutents. In analyzing fertilizers, only the jxitash. phos- phoric acid, and nitrogen are considered, these three being often spoken of as the fertilizing constituents. In fertilizer analysis, it is cus- tomary to carry out separate determinations of the jihosphorie acid soluble in water (mono-cal- cium phosphate), of 'reverted' phosphoric acid — i.e. that soluble in a standard solution of am- monium citrate (di-calcium phosphate), and of the insoluble form (tri-calcium phosphate). The soluble and reverted forms are more readily available to plants than the insoluble form, and arc valued at a higher price. In eomjilete analy- sis of soils, other mineral ingredients besides the potash and phosphoric acid are determined, such as magnesium, calcium, sodium, manganese, iron, alumina, and silica, and also the hunms. The latter is a very important constituent of soil in determining its fertility, ability to retain mois- ture, and to support biological changes which render the soil constituents available to plants. -Mechanical analysis 'of the soil is also made, in which the sample is separated into particles of different sizes by means of water, and the per- centage of each grade ascertained. The value of an agricultural soil depends to a considerable extent iipon its mechanical condition, as shown by tliis analysis, since this largely governs its capacity for moisture, capillarity, suitability for certain crops, and other qualities. In the exam- ination of soils, there have been many attempts to estimate the amount of the fertilizing ingre- dients present in forms available to plants. This is done by extracting the soil with weak acids and analyzing the extract, or by growing plants in pots'of the soil and analyzing the crop. Impor- tant as this matter is in determining the fertiliz- ers needed by soils, no method has yet been de- vised which is entirely reliable and satisfactory. Of the organic constituents of plants, those of most concern to the agricultural chemist are the so-called food constituents, which determine the value of the plant as food for animals or man. These may be divided into the nitroge- nous, or those containing nitrogen, and the non- nitrogenous substances. The nitrogenous are groui)ed under the name of protein, and include all)uininoids, eontaiiiing about 15 to 18 per cent, of nitrogen, the amides, and a variety of other bodies. Of the non-nitrogenous constituents, the most important are ( 1 ) the fats and oils and (2) the carbohydrates, including starch, sugars, pentoses, cellulose, fibre, etc. The protein of phmts is estimated by determining the nitrogen and multiplying the result by fl'4. "n the ns- s>nnption that tile protein constituents average about 10 per cent, of nitrogen. As this does not always hold true, the result is subject to slight error. In determining the fats, the mate- rial is extracted with ether, in a special extrac- tion apparatus, the ether expelled, and the resi- due weighed. This is not jnire fat. but contains also the waxes, ehloidi)hyll. lecithin, and some other bodies in small iiuantities. The fibre or cellulose is usually determined separatidy from the other carbohyilrates. This is (Ume by dis- solving out the other constituents of the plant with dilute alkali and acid, and weighing the residue, a correction being often made for the remaining traces of nitrogen and a.sh. As a large variety of other carboliydrates are usually liresent. wliieh are of similar feeding value, they are not di'lermiiied individually, except for spe- cial purjwscs. but are grouped with the organic acids and some other substances aliout which little is known, under the general head of nitro- gen-free extract. This is done on the supposi- tion that everything else has been accounted for in the water, ash, fat. protein, and libre deter- mined separately: and hence the dillerence be- tween the sum of the ])ercentage amounts of these and 100 represents the nitrogen-free ex- tract. Accurate methods have liecii worked out for determining the sugars, starches, jientoses, galactose, etc., separately, and these are used for special analysis. For example, in studying sugar-producing plants, the sugar is determined ery exactly. The principal organic acids in plants are oxalic, malic, citric, and tartaric, and these are determined on occasion, as in analysis of fruits, beverages, and some vegetables. In the analysis of dairy products, which comes within the scope of the agri<'ultural chemist, the ]irincipal sul)iects are milk, butter, and cheese. In milk analysis, the specifii' gravity (by lac- tometer), water, total solids (dry matter), fat, casein, sugar, and ash are determined, the fat being the constituent considered especially, as showing the richness of the milk and its value for butter and cheese making. (See ^Iii.k; Patrvino.) Butter is analyzed mainly with a view to detecting adulteration with oleomarga- rine, renovated butler, etc. Cheese is examined for water, fat, nitrogen, and ash, the principal objects being to determine its food value and to detect adulteration. There is a long list of other substances which come within the scope of the agricultural chemist for analysis, such as fungicides and insectici<les, human foods and lieverages, tanning materials, etc., which can only be referred to here. In dairying, the investigations of agricultural chemistry have been far-reaching in their results, largely modifying dairy ))ractice in a numlier of resjiects. For example, lialicock has worked out a rapid, simple, and accurate method of testing milk and cream as to their fat content. This test has come into very general use, and has not only changed the method of paying for milk at creameries and cliee.se factories, but led to the selection of cows giving richer milk. The same chemist, with Russell, a bacteriologist, has niadi' I'laborate studies of the ripening of cheese, and has discovered an inherent ferment in milk whose presence is held to account for most of the characteristic changes during ripening. The inspection or control work, which is now carried on in nearly every country, has afforded agriculturists needed protection in the purchase of fertilizers, feeding stuffs, and the like, and reduced the traffic to n business basis. The per- centages of essential constituents in these mate-