Preparation of Hypoplwspliates. 589 



a test tube submerged m warm water, inserting the rod 

 until its knob rests on the bottom of the tube, and finally 

 transferring the whole to a jar of cold water, taking care 

 to hold the rod in the center of the phosphorus until the 

 latter has hardened. When completely cooled the stick 

 of phosphorus is drawn out of the tube by a pull on the 

 imbedded glass rod. In our work the sticks of phos- 

 phorus were about 3-5 inches long by 0-65 inch in diameter. 



The jar is charged with about a liter of water and any 

 convenient amount of sodium carbonate, usually about 

 250 grams. It is immaterial whether the salt is in solu- 

 tion or not. The cover and suspended sticks of phos- 

 phorus are then put in place, and the corks adjusted so 

 that less than one centimeter of each stick projects from 

 the liquid. As the exposed area of the phosphorus grad- 

 ually becomes reduced by oxidation and solution this 

 adjustment has to be repeated, ordinarily at intervals 

 of two or three days. Control over the rate of the reac- 

 tion is maintained by regulating the access of air to the 

 interior of the jar. Several extra holes in the cover are 

 provided for this purpose and these are partly closed 

 with stoppers to the extent necessary to give a satisfac- 

 tory rate. Too high a rate is apt to result in spontaneous 

 ignition and consequent melting of the exposed portion of 

 some of the sticks. The apparatus should be set up in 

 some cool place, such as a cellar, and shielded from drafts, 

 which have a tendency to accelerate the reaction. A 

 convenient way of protecting the apparatus against 

 drafts and accidents is to cover it with a large bell jar, 

 taking care to leave a small opening for the entrance of 

 air. 



As the oxidation proceeds any sodium carbonate which 

 was still undissolved at the start passes gradually into 

 solution and the alkalinity steadily decreases. From 

 time to time samples of the liquid are withdrawn with a 

 pipette (inserted through a special hole, usually kept 

 stoppered, in the center of the cover) and tested with 

 Congo Red. 9 When the turning point of this indicator 

 is reached, the cover and suspended sticks of phosphorus 

 are simply transferred to another jar of the same size, 



9 Methyl Orange may be used instead of Congo Eed. The hydrogen-ion 

 concentration of a pure solution of acid sodium hypophosphate is slightly 

 nearer to the turning point of Congo Eed than to that of Methyl Orange, 

 but it is doubtful whether this difference is of any importance here. 



