VOLUMETRIC ANALYSIS, in chemistry, consists in submitting the substance to be estimated to certain characteristic reactions, the chemist employing for such reactions liquids of known strength, and from the quantity of liquid employed to induce the reaction, determining the weight of the substance to be estimated by means of the laws of equivalence. The idea of this method first suggested itself to Gay-Lussac in consid ering how most readily to determine the amount of silver in an alloy of that metal and copper; but the method itself did not come into general use till within the last 30 years. The liquid reagents of known strength are called standard solutions; and the amount employed may be estimated either by weight or by volume, but the latter being the easiest of application, is universally employed; and hence this method of analysis, based on the use of standard solutions, is called volumetric analysis. In order that a reactioa may be applicable in volumetric analysis it mast satisfy the two following conditions, (1) It must not occupy much time; and (2) the termination of the reaction must Lai easily recognized and unmistakable to the eye. The necessity that these conditions should be fulfilled, very much limits the the number of volumetric processes. In addition to the ordinary chemical appar atus, this kind of analysis requires gradu ated glass vessels of different kinds for the measurement of the standard solutions. Of these, the most essential are: (1) Pipet tes, which are glass vessels of the form of figs. 1 and 2, intended for the delivery of the standard solution. Fig. 1 is provided with a single mark upon the neck, while fig. 2 is divided and graduated through its whole length, the division being always made into cubic centimeters c.), accord
ing to French scale; (2) Flasks graduated for the contents in various sizes from one tenth of a liter to five liters, and used for the preparation of standard solutions; (3) B-arcftes, or graduated tubes for measuring the liquids used in an analysis. The bur ette was invented by Gay-Lussac; hut since his trine, various modifications have been proposed, the best of which, for gen eral purposes, is that which is known as Mohr's burette. It is shown in fig. 3; and its lower part is attached to an ind in-rubber tube and spring-clamp or clip (quctsch-halin). Its principal advantages over other forms of the instrument are, that its constant up right position enables the operator at once to read off the number of degrees of stan dard (or test) solution used for any analysis, while the quantity of fluid to be delivered can be most accurately regulated by the pressure of the thumb and finger on the clamp; moreover, as it is not held in the hand, no error is likely to arise in the measurement from the heat of the opera tor's hand. The greatest drawback to it is that it cannot be used for those test solutions which decompose india-rubber.
The standard solutions, known also as test or titrated solutions (from the French word tare, which signifies the standard of a coin), may be divided into (1) such as are imme diately prepared by weighing a substance of known composition, dissolving it, and diluting it to the required volume; and (2) such as are prepared by approximate mixture and subsequent exact analysis. The preparation of the first kind requires no description ; for the preparation of the second kind, we must refer to the article ANALYSIS, VOLU