Page:The New International Encyclopædia 1st ed. v. 04.djvu/660

CHEMISTRY. 578 CHEMISTRY. refinpinent of methods, and a ^reat deal of invos- tijralion has had purely that aim. The field covered has l>een very broad, and has not always heen strietly chemical. For example, the discovery of the ability of leguminous plants (clovers, peas, and the like) to appropriate to their use the free jiitrofren of the atmosphere, and thus, under cer- tain conditions, to enrieh the soil with nitrogen (the most expensive fertilizing element) from the air. was made by a German agricultural chemist, who also demonstrated the agency of bacteria in bringing about this a.ssimilation. See also Oree. Maxiiiing : Rotation' of Crops. RiuLiOGKAPiiY. Among the more important treatises on agricultural chemistry, the following may be mentioned: .Johnston, Lectures on the Application of Chemistry and Geology to Agri- culture (New York, 1850) ; .Tohnson, llow Crops Feed (Xcw York, 1000) : Johnson, flow Crops Grow (New York, 11)00) ; Storer, Agriculture in Some of Its Relations uith Chemistry (Xew York, 1897) : Tiley, Principles and Practice of Agricultural Analysis (3 vols.. Easton, Pa., 1804- 97) : DehOrain, Traits de chimic agricole (Paris, 1892) : Sachsse, Lehrbuch dcr Agriculturchemie (Leipzig, 1888) : Mayer, Lehrbuch der Agricul- turchemie (Heidelberg. 1895). See Food: and the special articles upon the principal foods. CHEMISTRY, Analytical. See Analysis, Chemical, ilany special processes of anal.-tical chemistry may be found described under the names of the substances in connection with which they are usually employed. CHEMISTRY, Organic. See Chemistry; Valency; Caruon Compounds; Stereochemis- try; Hydrocarbons: Alcohols: Aldehy'DES; ICetones; Ethers: Esters; Amines; Amides; Phenols: Diazo-Compoinds; Carbohydrates; Alkaloids, etc. All the more important organic compounds may be found described under their special names. CHEMISTRY, Physical. See Avogadro's EfLE; Molecules — Molecltlar Weights; Re- action ; Solution ; Dissociation : Thermochem- istry': Electrociiemlstry: Piiotochemi.sthy; Evapor.vtion ; Distillation ; Boili.ng - Point ; Melting-Point: Critical Point: Acid.s, etc. CHEMISTRY, Physiological. One of the biological sciences, having for its object the study and investigation of the manifold chem- ical processes taking place in living organisms, both .animal and veget.able. Physical, or me- chanical, physiology deals with those functions of living organisms explainable by physical laws and studied by physical methods. Chemical jihysiology. or physiologi<'al chemistry, deals with those functions exjilainable by chemical laws and studied by chemical methods. In the study of physiological chemistry, therefore, the facts to be collected and the methods pursued are al- most wholly cheiiiical, while the application is purely physiological. In the early days of physiological chemistry, energy was devoted mainly to the sintple study of chemical composition. The various tissues and organs, especially of the higher animals, were analyzed, their chemical composition ex- amined, and the chemical nature of the various proximate principles occurring in these tissues ascertained. It was found that twelve chemical elements enter into the composition of all living organisms — viz. carbon, nitrogen, hydrogen, oxy- gen, sulphur, pliosphorus, chlorine, sodium, po- tassium, calcium, magnesium, and iron — while more recently iodine has been found widely dis- tributed in organic combination. The first si.x of the above elements enter mainly into the inake-ui) of the organic substances of the living body, while the last six occur chiefly as inorganic or mineral corapoimds. Sulphur and phosphorus, however, are especially characterized l>y the fact that they are widely distributed in organic combination — that is, as an integral part of complex organic com]ioimds, as ]iroteids. niicleo- ]irotcids. and various crystalline substances — while at the same time in oxidizeil form as sul- phates and phosphates of the alkalies and alkali earths, they are ever present as part of the inorganic salts, or mineral matter, so abundant in animal and vegetable tissues. Iron likewise occurs both in organic combination, as in fer- ruginous nueleo-proteids and in the pigment of the red blood-corpuscles, and in the form of simple iron salts. The ideas of pliysiologists were revolutionized, and physiological elicmistry took on new dignity, when it was seen that the various chemical substances — both simple and complex— formed in the tissues of living organ- isms could be ccmstructed in the labcu'atory by comparatively simple methods. ( See Chemis- try. ) As a result, there rapidly developed great activity in the study of the chemical nature and chemical relationship of the organic compi>unds occurring in the body; methods were devised for producing them artificially: their genetic rela- tionshiiis were traced out; an<l much light was thrown tipon the conditions attending their for- mation in the body. To-day the study of the chemical ((mstitution of the various end-prod- ucts of catabolism formed in and excreted from the body has given most useful information re- garding .a host of chemical jirocesses iii-<Mirring in the organism, and has enabled the physiologist to trace out many of the individual steps in the breaking do^'n of complex organic material. In other words, chemical methods and simple chem- ical principles are quite suflicient to explain the nattire of the many processes going on in liv- ing organisms by which the life and activity of the organism are maintained. The various chemical ]irocesses characteristic of living organisms may be divided into two main groups — viz. synthetic and analytic; i.e. building up and breaking down. Synthetical processes are most prominent in the vegetable kingdom. The pl;int-ccll alone has the power of building up complex organic compounds out of simple elementary substances. The most strik- ing illustration of this constructive power is seen in the formation of protcid or albuminous material. This imjiortant constituent of every living cell, in part the chemical basis of proto- plasm, originates solely through the synthetical power of the jilant-cell. The carbonic a<'id of the atmosphere furnishes the carbon, hydrogen is drawn from the moisture, nitrogen from am- monia or nitrates in the air and water, oxygen from the air. sulplmr and phosphorus from the stilphates and |>liosphates of the soil. From these elements proteid. the most complex organic substance known in nature, is constructed. As indicative of its chemical composition, we ascribe to it various formuhe according to its exact nature, for there are many different pro- teids in both the animal and vegetable king-