1864.] Dr. Marcet on a Colloid Acid of Urine. 5 



Five out of the six analyses were made with the acid slightly coloured, to 

 avoid possible inorganic impurity from the use of animal charcoal. In analysis 

 No. VI. the acid had been treated with animal charcoal, and in this case 

 the percentage of lead was a little higher. It is possible that 33*7 is not 

 the exact percentage of acid in the insoluble lead-compound, although it 

 cannot he far from correct ; but when the difficulty of obtaining the lead- 

 precipitate in a pure condition is taken into account, I think it will be 

 admitted that the results of these analyses approach each other closely 

 enough to show that the lead-precipitate of the colloid acid is a definite 

 chemical compound. Adopting the number 33- 7 as the percentage of 

 acid, the equivalent weight of the acid and of the compound will be 



PbO 111-57 



Acid 56-/0 atomic weight of acid. 



168-2 atomic weight of compound. 



To prepare the baryta-compound of the colloid acid, I began by de- 

 composing with sulphuric acid a known weight of the lead-salt ; and by pro- 

 ceeding as in the case of the analysis of the lead-compound, the amount 

 of the colloid acid present was determined. The acid was entirely washed 

 through the filter along with some free sulphuric acid, and I treated the 

 acid filtrate with carbonate of baryta, the mixture being heated for four 

 or five hours, and filtered the next day ; the precipitate on the filter was 

 finally washed with hot distilled water for from four to six days, and even 

 after this lapse of time the washings still contained a trace of baryta. I shall 

 only report two out of several of these analyses, as in the others the de- 

 ficiency of baryta dissolved was obvious. I have calculated the atomic 

 weight of the acid from the baryta-compound which yielded most baryta, 

 as follows 



Analysis No. I. 



per cent. 



Compound of colloid acid and f BaO 0-4607 .... 72'2 



baryta 0-6382 1 Acid 0-1775 .... 27'8 



100-0 

 Analysis No. II. 



Compound of colloid acid and f BaO 0-5950 65'7 



baryta 0-9058 \Acid 0-3108 34-3 



100-0 



The atomic weights derived from analysis No. I. are 



BaO . 76-39 



Acid . . .... 29-5 



Compound 106-0 



