592 PROCEEDINGS OF THE AMERICAN ACADEMY. 



was so perfectly made that it was nearly gas tight with no lubricant. 

 Nevertheless, in addition, nitrogen was maintained at atmospheric pres- 

 sure on the far side of the valve, so that the slight leakage produced a 

 slow reverse current of nitrogen through the valve into the pump by 

 way of the bulbs M and N. 



Under as low a vacuum as could be obtained with the pump the tri- 

 bromide was first distilled from D to G by surrounding D with boiling 

 water and G with ice water. A small residual fraction was left in D, 

 in order to make certain the elimination of phosphorus acids and pos- 

 sible oxybromide. During this distillation any phosphorus which had 

 originally distilled into the tube F and still remained uncombined was 

 converted into tribromide by the excess of bromine. A second similar 

 distillation from G to J and K followed, with rejection of the last few 

 grams in G. The material invariably contained an excess of bromine 

 at this point. The capillary tube H was now sealed with a blowpipe 

 and the flasks J) and G were thus disconnected from the apparatus. 

 Next the bulbs M and N were cooled with ice and the tribromide in J 

 was boiled while the bulb K was gently warmed. The vapor from J in 

 bubbling through the warm liquid in K carried with it all the excess of 

 bromine in both bulbs. Furthermore it is probable that if the tribro- 

 mide contained a trace of hydrobromic acid, the latter substance was 

 eliminated at the same time as the bromine. The distillate collected 

 in M and N as tri- and pentabromide. As soon as ten grams of mate- 

 rial had been distilled from J and K the residue, amounting to consid- 

 erably more than one hundred grams, was nearly colorless ; nevertheless 

 five times as much more was distilled into M and N before this part of 

 the apparatus was sealed off at the capillary L. Thus when the stop- 

 cock was closed, the impure distillate was entirely cut off from the 

 remainder of the apparatus. 



The bulbs 1 to 8 were then exhausted by opening the stopcocks of 

 the U -tube U and at the point T, while E, was closed. The U-tube con- 

 tained resublimed phosphorus pentoxide to prevent the possibility of 

 back diffusion of moisture into the bulbs. The valve P, into which a 

 piece of soft iron had originally been sealed, could now be pulled from 

 its seat by means of a magnet so that the bulbs J and K were connected 

 with the pump through the bulbs 1 to 8. 



In distilling the remainder of the tribromide into the small bulbs the 

 one nearest the pump was filled first by surrounding it with ice water, 

 while the other seven were immersed in beakers filled with boiling 

 water. As soon as bulb 8 was three-fourths filled with material, bulb 7 

 was cooled with ice water, and so on until all were filled. All the 

 residual material in J and K was distilled into bulb 1. 



