On Tribasic Phosphoric Acid. 171 



Thomson. had found it to be as 



100 : 163.4 

 while H. Rose had determined it as 



100: 114 

 These figures, being used by different chemists of the time, 

 deviated far enough to make a new investigation desirable. 

 Dulong published in the year 1816 (Ann. Ch. et Phy. vol. 

 2) an essay in which he stated that the proportion of phos- 

 phorus to oxygen in phosphoric acid was as 100:124.8, and 

 that the oxygen in the phosphoric acid was to the oxygon in the 

 phosphorous acid as 5 : 3 ; also that the atomic weight of phos- 

 phorus, reduced to our present figure of oxygen, was 32.<>4s. 



I will here give the figures, which since the discovery of 

 phosphorus have been used at different times by different 

 chemists to represent its atomic weight : 



So H=l=9 32 16 31.436 3.699 



15.777 15.7 31.4 (8 fig.) 

 So 0=1.100.1000=167.512 4 3.9308 

 39.30 1.50 19.65 196.155 

 46.155 196.143 19.62 196.153 

 392 196.0285 (13 fig.) 

 They are in all 23, varying from 1.5 to 392.3, and offer- 

 ing a variety, out of which almost any one might have 

 selected a number that would suit his particular views and 

 tastes. 



Up to this year, 1816, only twelve phosphatic minerals were 

 known, two of which only were analyzed as to their amount 

 of phosphoric acid. In the same year occurs the publication of 

 Beraelius' great and masterly essay (Ann. Ch. Phy. vol. 2) 

 " On the composition of phosphor! <■ and pjioxplurrous acids^ 

 and tln'ir combination with salifioJ>l> /><tses." This essay fin- 

 ishes the first epoch in the knowledge of phosphoric acid, the 

 second reaching to Graham's investigations, L 834, and the third 

 not having been yet concluded. Berzelius, to whom Dulong's 

 investigations were not unknown, judged, from the results of 



