compounds from thiophosphoryl fluoride, it was evident from the relatively large quantity of arsenious sulphide invariably produced, that the method, even apart from the manipulative difficulties of working with sealed tubes containing gas under pressure, was neither a convenient nor an economical mode of preparing the new substance. If arsenic trifluoride is heated with phosphorus pentasulphide in a sealed glass tube, the gas evolved consists mainly of silicon tetrafluoride. Lead fluoride, however, readily reacts, on heating it with phosphorus pentasulphide, producing thiophosphoryl fluoride in considerable quantity P2Sь + 3PbF2 = 3PbS + 2PSF3. A mixture of red phosphorus, sulphur, and lead fluoride also gives rise to thiophosphoryl fluoride, but if the materials are used in the proportions required by the above equation, the reaction is extremely violent. It may, however, be moderated by using a large excess of lead fluoride. The mixture should be placed in a thin layer in a glass tube of narrow bore and which is gradually heated from behind forwards, so that the gaseous product as it is formed passes over the cold anterior portions of the tube and materials. Bismuth trifluoride may be used instead of lead fluoride in the reaction, but in this case a brass tube must be employed, as the temperature at which the gas is evolved is considerably higher, and large quantities of phosphorus trifluoride are apt to be simultaneously formed. On the whole, we found that the most convenient method is to heat a mixture of lead fluoride and phosphorus pentasulphide, but in order that the gas shall be obtained pure, certain precautions are absolutely necessary. Thiophosphoryl fluoride is readily altered by contact with air and moisture: hence it is necessary that the materials should be perfectly anhydrous, and that every trace of free oxygen should be absent. Moreover, as the gas is readily decomposed by heat, it is desirable that it should be produced at the lowest possible temperature. The best method of procedure is as follows: A quantity of freshly prepared phosphorus pentasulphide, made from washed and perfectly dry amorphous phosphorus and powdered roll sulphur, is quickly pounded with the requisite quantity of pure freshly fused lead fluoride, and the mixture is placed in a thin uniform layer in a dry leaden or "composition" tube, open at both ends. One end of the tube is fitted with a caoutchouc cork and glass delivery tube, whilst the other is attached to an apparatus yielding a supply of pure dry nitrogen. The air within the tube is rapidly swept out by the dry nitrogen, and the tube is gently heated in order to get rid of any sulphuretted hydrogen produced by the action of atmospheric moisture on the phosphorus pentasulphide. When the tube is completely filled with nitrogen, the current of this gas is stopped and the leaden tube is heated from behind forwards by a small Bunsen flame. The reaction begins at about 170°, and as it is advisable to keep the temperature as low as possible consistent with the production of the gas, it should not exceed 250°. The gas is collected over dry mercury and may be stored in a glass gas-holder. The gas-holder should contain a few fragments of quicklime, the pores of which should be freed from air by passing small quantities of dry nitrogen into the gas-holder and repeatedly exhausting by means of the Sprengel pump. The thiophosphoryl fluoride is not allowed to pass into the holder until a sample is wholly absorbed by a dilute solution of potash or ammonia. In order to get rid of the small quantity of nitrogen adhering to the lime, as soon as two or three cubic centimetres of gas have entered the holder, the latter is connected with the Sprengel pump and the gas and nitrogen sucked out, this operation being repeated twice or thrice. The rest of the gas is passed into the holder, and after standing for a day or so over the lime, which removes the phosphorus fluoride and any traces of silicon tetrafluoride, is pure thiophosphoryl fluoride. Determination of Vapour-density.-A bulb of about 240 c.c. capacity and fitted with tubes and stopcocks, as seen in Fig. 1, after being cleaned and weighed, is placed in a bath of water and filled with dry nitrogen. The bulb is then connected with a small mercury gasholder, containing thiophosphoryl fluoride, made and purified as above described, and the nitrogen is slowly displaced from below upwards by the thiophosphoryl fluoride. The exit-tube of the bulb is attached to a piece of glass tubing, which dips a short way under mercury, so as to cut off the direct connection with the air. The bulb is immersed in the bath nearly to the level of the stopcocks, and a current of cold water, carrying with it a stream of air-bubbles. is allowed to enter at the bottom of the bath, and flow away at an opening near the top. The stream of air-bubbles is sufficiently strong to keep the mass of the water in circulation, and thus tends to render the bath of uniform temperature. When all the gas has passed over, the cocks of the bulb are turned, the tube dipping under the mercury removed, one cock momentarily opened to equalise the pressure, and the temperature of the bath and the height of the barometer noted. The dried bulb, after standing in the balance-case for about an hour, is then re-weighed. To determine the amount of the residual nitrogen, the entry-tube of the bulb (both stopcocks being closed) is connected by means of caoutchouc tubing with a large burette containing a dilute solution of pure caustic potash. The potash is caused to fill the caoutchouc tube and the entry-tube of the bulb up to the stopcock. The stopcock is next opened and the potash allowed to enter the bulb. The gas is slowly absorbed, the bulb being meanwhile immersed in a vessel of water at a constant temperature. When the absorption is complete and the contents of the bulb are brought to the temperature of the water, the levels of the liquid in the bulb and burette are equalised, and the burette reading taken. The burette is then raised, and the stopcock of the exit-tube of the bulb is carefully opened. The level of the potash solution within the bulb rises until it reaches the stopcock, which is then closed, when the levels are again equalised and a second reading on the burette taken. The difference between the two readings gives directly the volume of the residual nitrogen at the temperature of the bath and under the atmospheric pressure. The details of two experiments carried out in this way are as follows: : I. Capacity of bulb at 15.8° and 776 mm....... Volume of residual nitrogen at 11:3° and .... Weight of thiophosphoryl fluoride...... Volume of gas + residual nitrogen at 0° and 760 mm..... Volume of residual nitrogen at 0° and 760 mm. Volume of thiophosphoryl fluoride..... 157-29 c.c. of thiophosphoryl fluoride weigh. 1000 c.c. of thiophosphoryl fluoride weigh... Vapour-density (H1) 59-66. II. = 239.86 c.c. Vapour-density (H1) 59-56. 238.81 c.c. 195.95 99 1.0457 gram 5:3355 29 The calculated vapour-density of PSF, is 60·0. Analysis of Thiophosphoryl Fluoride. The solution of the gas in the dilute potash was transferred to a 500 c.c. measuring flask, and the bulb carefully washed out and bromine-water added to the liquid until the colour persisted after repeated shaking, when the solution was diluted to the mark. In order to determine the sulphur, an aliquot portion of the solution was acidified with hydrochloric acid and mixed with barium chloride and the barium sulphate weighed. To obtain the amount of phosphorus, a second aliquot portion of the liquid was treated with ammonium molybdate solution in the usual manner, and the precipitate converted into magnesium ammonium phosphate and weighed as pyrophosphate. The results were as follows: I. One-fifth of a solution containing 0.8408 gram of gas gave 0-3223 gram barium sulphate. A second fifth gave 0.1557 gram magnesium pyrophosphate. II. One-fifth of a solution containing 10457 gram of gas gave 0-3992 gram barium sulphate. A second fifth gave 01924 gram magnesium pyrophosphate. Properties of Thiophosphoryl Fluoride.-At ordinary temperatures thiophosphoryl fluoride is a transparent, colourless gas, which, under the application of about 10 to 11 atmospheres pressure, condenses to a colourless liquid. Neither the gas nor the liquid acts to any appreciable extent on dry glass at ordinary temperatures. In air or oxygen the gas is spontaneously inflammable, and its oxidation products have a disagreeable, irritating smell, in which that of sulphur dioxide can readily be detected. Under the action of heat or the electric spark the gas is readily decomposed, with the separation of sulphur and phosphorus and the formation of phosphorus fluorides. If the decomposition be effected in a glass tube heated to a sufficiently high temperature, the gaseous product eventually consists entirely of silicon tetrafluoride. Thiophosphoryl fluoride has no action on mercury, oil of vitriol, carbon bisulphide, or benzene. In ether, it is soluble to some extent, and the solution burns with a greenish flame. The gas is not readily dissolved by water, and dilute solutions of potash, soda, and ammonia |
