Gooch and Jones — Estimation of Boric Acid. 35 



From our experience it seems obvious that the demand for 

 this amount of calcium oxide arises from an excessive use of 

 nitric acid in the retort and the consequent modification of 

 conditions in the distillate. Fortunately this difficulty may be 

 avoided by the use of a little phenolphthalein as an indicator 

 in the retort and care to limit the addition of nitric acid to the 

 amount required to produce distinct acidity. The addition of 

 a drop of the acid and another of the indicator should be 

 repeated once or twice during the distillation to insure the 

 replacement of the acid volatilized from the salt slightly 

 decomposed in the process. The effect of much nitric acid is 

 bad, not only because it neutralizes the calcium oxide when it 

 passes to the distillate, but because when it is used a tendency 

 is developed on the part of the dried mixture of calcium 

 hydroxide and borate to puff explosively if this ignition is 

 begun as soon as the residue is dry. If the residue is heated 

 gradually and as strongly as possible over a radiator before the 

 flame is actually applied to the crucible, no such action takes 

 place ; we are disposed to attribute it to the effect of the 

 nitrate and nitrite, produced by the absorption of nitrous 

 fumes in the lime, upon the alcohol or other organic matter 

 retained by the lime in the evaporation and drying unless the 

 latter process is prolonged at high temperature. 



That good results may be obtained with small amounts of 

 calcium oxide provided care as to the use of nitric acid and the 

 conditions of ignition be taken, is shown by the figures of the 

 original description and by the following experiments, in which 

 phenolphthalein was employed as an indicator and the residue 

 heated strongly over the radiator before actual ignition. 



CaO taken. 



B 2 3 taken. 



B 2 3 found. 



Error. 



grm. 



grm. 



grm. 



grm. 



2-3405 



0-1788 



0-1792 



+ 0-0004 



1-7620 



0-1790 



0-1785 



— 0-0005 



2-1757 



0-1824 



0-1840 



+ 0-0016 



2-5656 



0-1788 



0-1786 



— 0-0002 



These results are accurate within reasonable limits. On the 

 other hand, without care to ignite gradually we have noted 

 errors of from 0*0030 grm. to 0-0060 grm. in the process other- 

 wise conducted similarly. Doubtless the use of large amounts 

 of calcium oxide as suggested by Moissan may serve the pur- 

 pose of diffusing the explosive mixture through a mass of 

 inert matter sufficient to prevent violent puffing, but care to 

 heat over the radiator as strongly as possible before opening 

 the flame directly to the crucible answers the same end. The 

 difficulty does not exist when acetic acid is used in place of 

 nitric acid, though even in this case it is safer to use the 

 radiator in the first stages of heating, thus avoiding the danger 

 of mechanical loss by too rapid ignition. 



