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Home > ALKALIMETftY. the alkalies of commerce...
Previous Next The best candle and soap tips online! ALKALIMETftY. the alkalies of commerce depend their value, and the amount necessary to use in solution to boii or make a soap. To determine the quantity of real alkali the lyes may contain, it is obvious that a rapid and easy method is very desirable, and among ths numerous means to this end it is the desire of the writer to give the least elaborate, and to simplify the description as much as possible. The hydrometer of Baumd, though a valuable instrument in determining the density of a fluid, will not give an accurate test of the strength of a caustic alkali, as all the impurities dissolved with the solution tend to make it heavier. So it would show butaninperfect resiilt,for it would not indicate the amount of alkali, but the density or specific gravity of the fluid, which might be a solution of culinary salt, or a mixture of several salts, and it is a useful instrument only when the proper preparation haa been given to the lyes, and they have been brought into a state of causticity and purity necessary for the eaponification of fats. Then it is exceed-iugly handy. To ascertain the true condition, other and more scientific tests are necessary. Analysis by Measure, or Volumetric Analysis. Though a simple process to the expert, it yet requires some practice and skill, for, as we have remarked, the alkalies of commerce are contaminated with so many foreign ingredients that their testing requires great exactness, and moreover, the methods of different chemists vary with each, though giving the same results. From these processes we shall try and select the simplest. Alkalimetry was until quite recently a purely technical operation, when it assumed a scientific basis, and has developed into an almost perfect prvicess, which simply in its entire operation consists in the neutralization of the alkaline base with an acid of a certain strength. The operation itself is called titration from the acid which has a certain titre} that is, a certain weight according to the contents. A certain weight of acid corresponds to a certain 168 TECHNICAL TREATISE ON SOAP AND CANDLES, weight of alkali,BO that these measures may finally he reduced to weight. Mohr expresses himself as follows: "But one weighing is only performed where formerly many had been needed. The accuracy of the one normal weight ia repeated in every experiment made with the liquid thus prepared. With one litre of test-acid, several hundred estimations may be made. The producing of two or more litrea of test-fluid requires no more time and no more weighing than one litre. The weighing can therefore he performed whenever time and leisure admit." Besides the acid we require certain instruments by means of which the acid is added to the solution of the body under investigation. Anc as here a decomposition ia always carried to its limits, and not as in case of common analysis with a surplus of the precipitation, these implements must permit of a very regular flowing oil' by drops. They are two, the burette and the pipette. THE BURETTE. Thia instrument has been brought into use in various forms, but we give the preference to the clip (30m press ion, stopcock) burette of Mohr (Fig. S), for its simplicity and convenience of manipulation. It consists of a straight cylindrical glass tube, of not too thin Bides, which is graduated into Łor TVcubic centimetres (0.054or 0.027 fluidrachm), At its lower eni it is drawn out to a somewhat distended point to allow a gam tube to be drawn over it and securely fastened. The india-rubber tube is about 40 millimetres (1.57 inches) long, and is, if necessary, tied with a strong silken thread. In the lower end a glass tube drawn out to a tine point is inserted, which as it has only to bear a certain strain of the liquid column while the compression-stopcock is opened it holds easily without any fastening. The gum tube is closed by means of a clip; this latter IB made of brass wire, hard drawn, of 8 to 3J millimetres (0.12 to 0.14 inch) thickness. To this end the wire, which is shown of its full size in Fig. 4, is bent into a 20 to 22 millimetre(0.78 to 0.86 inch) wide circle and the ALKALIMETRY. ends in the direction of the radius carried forth parallel. This circle is flattened upon a polished anvil with a polished hammer so as to obtain in this direction more elasticity. On one end is soldered a right angle piece of the same kind of wire. Upon the cut atf part, two smaller angles of the 170 TECHNICAL TEBAT10E ON SOAP AND CANDLES. ALKALIMETRY. IT! same wire are soldered. In a position of rest tha angles are lying ou each other. Aa soon as we press upon the handle-joints the angles open, and the gum tube relieved from pressure permits the liquid in the burette to flow out. Fier. 4 Previous Next
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