278 Mr. J. Prideaiix on the Composition 



it would be perfectly freed from hygrometric water, by re- 

 maining in a cold vacuum with sulphuric acid, I do not 

 know; but conceiving there must be a vapour of that acid, 

 which, however slight, must in the course of time settle more 

 or less on the crystals, and still more on the powder, a cur- 

 rent of warm dry air seemed a less objectionable mode. This 

 too required caution; for if the temperature reached any thing 

 approaching 212°, opacity appeared on some of the crystals, 

 and the salt used in this state was always in excess. About 

 140° seemed to answer very well, and in this the salt was kept 

 three or four hours ; the nitrate of lead being kept beside it, 

 that they might be equally dried. 



(3.) 13 J grs. of chloride of barium were precipitated by 

 8| grs. of oxalate of ammonia ; and 



(4.) 20| grs. of nitrate of lead by 9 grs. of sulphate of soda. 

 In both cases the anhydrous salt was in excess, and the 

 precipitation manifest and immediate on applying the test. 



All these experiments have been repeated as often as lei- 

 sure would allow, with materials prepared at different times, 

 and with identical results (except when, as above stated, there 

 were overdried crystals of the oxalate of ammonia). The 

 beam employed answers to the yi^dth of a grain ; the weights 

 are adjusted, by division and addition, from a standard eight- 

 grain, used for that purpose only ; and the salts were weighed 

 by the French method, first balancing the weight and then 

 putting the salt in its place. So far as confidence can be placed 

 in the results, Thomson's numbers seem nearer approximations 

 than those of Berzelius; according to which there should have 

 been in Experiment 1. an excess of -^-^-^ gr. of chloride of 

 barium = O'l'tS of sulphate; and in Experiment 2. an excess 

 of jQ^jj gr. nitrate of lead = 0*13 nearly of oxalate. 



The excesses in the 3rd and 4th Experiments correspond 

 so far with the tables of Berzelius ; they were not collected and 

 weighed, because the absence of hygrometric water could not 

 be depended on, though I can hardly believe the quantity 

 could be such as to account for so much precipitate. That 

 oxalic acid is almost exactly 4*5, I have no doubt ; but it may 

 be questioned whether azote is not under-rated in the " First 

 Principles ;" and as this is common to the two salts mutually 

 equivalent, and deficient in j-elation to the others, the differ- 

 ence would be well accounted for. This would interfere with 

 Dr. Front's law; but whilst the ablest chemists are at variance 

 on such simple experiments, we must be content with approxi- 

 mations. 



Phosphoric acid is stated by Berzelius to consist of 5 atoms 

 oxygen and 2 phosphorus: phosphorous acid, of 2 phosphorus 



and 



