Mauricheau-Beaupré has elaborated a volumetric method for the estimation of the phosphine in crude acetylene depending on its decomposition by a known volume of excess of centinormal solution of iodine, addition of excess of standard solution of sodium thiosulphate, and titrating back with decinormal solution of iodine with a few drops of starch solution as an indicator. One c.c. of centinormal solution of iodine is equivalent to 0.0035 c.c. of phosphine. This method of estimation is quickly carried out and is sufficiently accurate for most technical purposes.
In carrying out these analytical operations many precautions have to be taken with which the competent analyst is familiar, and they cannot be given in detail in this work, which is primarily intended for ordinary users of acetylene, and not for the guidance of analysts. It may, however, be pointed out that many useful tests in connexion with acetylene supply can be conducted by a trained analyst, which are not of a character to be serviceable to the untrained experimentalist. Among such may be named the detection of traces of phosphine in acetylene which has passed through a purifier with a view to ascertaining if the purifying material is exhausted, and the estimation of the amount of air or other diluents in stored acetylene or acetylene generated in a particular manner. Advice on these points should be sought from competent analysts, who will already have the requisite information for the carrying out of any such tests, or know where it is to be found. The analyses in question are not such as can be undertaken by untrained persons. The text-book on "Gas Manufacture" by one of the authors gives much information on the operations of gas analysis, and may be consulted, along with Hempel's "Gas Analysis" and Winkler and Lunge's "Technical Gas Analysis."
[APPENDIX]
DESCRIPTIONS OF A NUMBER OF ACETYLENE GENERATORS AS MADE IN THE YEAR 1909
(The purpose of this Appendix is explained in Chapter IV., page 111, and a special index to it follows the general index at the end of this book.)
AMERICA--CANADA.
Maker: SICHE GAS CO., LTD., GEORGETOWN, ONTARIO.
Type: Automatic; carbide-to-water.
The "Siche" generator made by this firm consists of a water-tank A, having at the bottom a sludge agitator N and draw-off faucet O, and rigidly secured within it a bell-shaped generating chamber B, above which rises a barrel containing the feed chamber C, surmounted by the carbide chamber D. The carbide used is granulated or of uniform size. In the generating chamber B is an annular float E, nearly filling the area of the chamber, and connected, by two rods passing, with some lateral play, through apertures in the conical bottom of the feed chamber C, to the T-shaped tubular valve F. Consequently when the float shifts vertically or laterally the rods and valves at once move with it. The angle of the cone of the feed chamber and the curve of the tubular valve are based on the angle of rest of the size of carbide used, with the object of securing sensitiveness of the feed. The feed is thus operated by a very small movement of the float, and consequently there is but very slight rise and fall of the water in the generating chamber. Owing to the lateral play, the feed valve rarely becomes concentric with its seat. There is a cover G over the feed valve F, designed to distribute the carbide evenly about the feed aperture and to prevent it passing down the hollow of the valve and the holes through which the connecting-rods pass. It also directs the course of the evolved gas on its way to the service-pipe through the carbide in the feed chamber C, whereby the gas is dried. The carbide chamber D has at its bottom a conical valve, normally open, but closed by means of the spindle H, which is engaged at its upper end by the closing screw-cap J, which is furnished with a safelocking device to prevent its removal until the conical valve is closed and the hopper chamber D thereby cut off from the gas-supply. The cap J, in addition to a leather washer to make a gas-tight joint when down, has a lower part fitting to make an almost gas-tight joint. Thus when the cap is off; the conical valve fits gas-tight; when it is on and screwed down it is gas-tight; and when on but not screwed down, it is almost gas-tight. Escape of gas is thus avoided. A special charging funnel K, shown in half-scale, is provided for inserting in place of the screw cap. The carbide falls from the funnel into the chamber D when the chain is pulled. A fresh charge of carbide may be put in while the apparatus is in action. The evolved gas goes into the chamber C through a pipe, with cock, to a dust-arrester L, which contains a knitted stocking lightly filled with raw sheep's wool through which the gas passes to the service- pipe. The dust-arrester needs its contents renewing once in one, two, or three years, according to the make of gas. The pressure of the gas is varied as desired by altering the height of water in the tank A. When cleaning the machine, the water must never be run below the top of the generating chamber.
