204 1)11. ROBERTS ON THE ESTIMATION 



the influence of yeast before fermentation begins, and the 

 density of the solution is thereby materially increased, 

 corrections had to be made on both these accounts before 

 the experiments could be fairly compared with those on 

 diabetic urine. In making the first correction cane sugar 

 was taken as C12 H^ 0^^ and grape sugar as C^a H^o Oi2- 

 In making the second correction allowance was made for 

 the increase of density in accordance with the tables pub- 

 lished by the authors of the report on " Original Gra- 

 vities." * 



Six solutions were made of cane sugar in water; two 

 containing 10 per cent, and the remaining four containing 

 respectively 8, 6, 4 and 2 per cent, of sugar. 



The mean co- efficient obtained from these six experi- 

 ments was 0"234. 



Twelve solutions were similarly made in a healthy non- 

 saccharine urine; two containing 10 per cent., three 8 per 

 cent., and tvv^o 2 per cent. The remainder contained 

 respectively 6, 4, i'4, i and o*6 per cent. These yielded a 

 mean co-efB.eient of 0'228 ; and the general mean for the 

 eighteen trials was a fraction under 0"23. These experi- 

 ments therefore confirmed the results previously obtained 

 with the volumetrical analysis as a standard. 



Equally correct results were obtained in operating on 

 weak solutions, containing only i or o*6 per cent, of sugar, 

 where the density lost was not more than 3 or 4 degrees, 

 as with solutions containing 10 per cent, of sugar, in 

 which the loss of density exceeded 43 degrees. 



Having examined the question experimentally, and fixed 

 the co-efficient from multiplied trials under varied condi- 

 tions, it was not without interest to examine a little more 

 closely the several items which go to constitute the " den- 

 sity lost" in fermentation, and to endeavour to arrive 



* Keport ou Original Gravities, by Professors Graham, Hofmaun and 

 lledwood, iu the (Quarterly Journal of the Chemical Society, 1853. 



