Chemical Preparations and Drugs. 55 



If, with prolonged combustion, the flame size should diminish owing to charring 

 of the tip of the wick, the vessel C and the lamp are taken out, after partly screwing 

 down the suction pump, lest the opening of the apparatus should drive the absorption 

 liquids back into the apparatus. The lamp is weighed as before; the asbestos wick 

 is pulled out by means of pincers, 2 or 3 mm., and the charred tip is cut off with 

 the scissors. A second weighing will show the loss of weight thus produced; the 

 apparatus is re-erected and the combustion continued. 



When a sufficient quantity of benzaldehyde has been burnt, the lamp is taken 

 out, and the weight of the consumed benzaldehyde is ascertained. After passing an 

 air current at moderate rate for some time through the apparatus, the joint is loosened 

 below the sphere G, and the water-jet pump is stopped. 



In order to remove any petroleum added and any soot that should have formed, 

 the absorption liquids are filtered through glass wool. For this purpose two glass 

 funnels, about 12 cm. diameter, are partly charged with glass wool after fitting a short 

 piece of rubber tubing provided with a pinch cock over the funnel tube. The funnels 

 are attached to the stand, and two Erlenmeyer flasks of about 500 and 350 cc. capacity 

 are placed under the funnels. The cylinder D is taken off, the short connections 

 between the two tubes are removed, and the content of each U-tube is emptied into 

 one of the funnels after opening the pinch cocks, the U-tube E being, discharged into 

 the larger Erlenmeyer. When the liquid has completely drained off, the pinch cocks 

 are closed, and each U-tube is rinsed with 15 cc. of water three times and the 

 cylinder D twice, this water being added to the funnel contents (the cylinder wash 

 water into E). If the beads on the funnels should not quite be covered with water, 

 a suitable amount of water is added; the pinch cocks are opened a few minutes 

 afterwards. This washing of the glass beads is repeated 3 times so that the liquid 

 will amount to about 300 or 200 cc. We now add 50 cc. of N/50 sulphuric acid to 

 each of the two Erlenmeyer flasks and also a few marbles, to ensure quiet boiling; 

 the flasks into which small funnels are fitted are then heated on asbestos wire 

 netting until the liquid has been concentrated down to 25 cc. After cooling we 

 titrate, after additionof a little phenolphthalein as indicator, with N/50 caustic potash 

 until the colour remains red; the amount of potash is noted. We then destroy the 

 red colour again by means of one or two drops of N/50 sulphuric acid. Now follows, 

 after addition of 5 drops of 10 per cent, potassium dichromate solution, titration with 

 N50 silver nitrate, first of the liquid from the U-tube F which served for control, 

 until a faint chromate colouring becomes visible, and then of the contents of the 

 second Erlenmeyer. 



In control tests, conducted in the same 4 way for ascertaining the chlorine contents 

 of the water and of the standard solutions, we used the same amount of caustic potash 

 and of silver nitrate as the contents of the U tube F had required (0.4 cc). It was 

 thus proved that the whole of the hydrochloric acid is really absorbed in the U tube E, 

 and that we need, in our calculations, only consider the silver nitrate that was wanted 

 for the contents of U tube after deducting the control amount. Since now 1 cc. of 

 N/50 silver nitrate corresponds to 0.00071 g. of chlorine, the chlorine contents of the 

 respective benzaldehyde would be: — per cent, chlorine = «• 0.071 /-§, where « denotes 

 the number of cc. of N/50 silver nitrate used and s the weight of benzaldehyde 

 burnt, in g. 



In order to check the reliability of the method we conducted experiments with 

 natural bitter almond oil, containing prussic acid and free of prussic acid, with artificial 

 benzaldehyde and with benzaldehyde of known chlorine percentage. 



