81 



COMMENTS BY ANALYSTS. 



G. ^f. Bnrtlrtt: The < inversion of the starch was carried out as outlined, no difficulty 

 occurring in tin- procedure. The aliquot for precipitation was obtained as follows: 

 After converting, neutralizing, and adding basic lead acetate the sample was made 

 u p to volume at about 35 C. To 100 cc at this temperature was added the 60 per cent 

 <>f sulphuric acid, cooled so that the volume of liquid contracted to 100 cc. It was 

 necessary to n.ol only to about 18 C. The sample for precipitation was taken when 

 the liquid hud contracted to the mark. Two determinations were made one by pre- 

 cipitating by the \\alker-Munson method (J. Amer. Chem. Soc., June, 1906,) and the 

 other following the method in Bulletin 107. The latter gave 11.83 per cent of starch. 



In determinm- crude liber the electric stove was used for boiling the 1.25 per cent 



crude liber, even though it is not to be ignited, and would prefer filtering on a weighed 

 platinum <_roorh filter. 



In calculating the suirar in chocolate by Dubois's method" it seems illogical to 



multiply (06) by l.Oor (x equaling the volume obtained by dissolving sugar in 



HH> cc "i her than by 105 plus the increase in volume due to the solution of 



the mgar. Tin- a- tually makes but little difference in the result, but the following 



ment of tin- formula -e.-ms preferable: 



(a-6)(l05+ f f ) 



' = per cent sucrose. 



111-., 



Where , ' increase of volume ..\\in^ loth,- solution of t ho sugar in water. In calcu- 

 the l.ido-.- ihe compleie formula read.-: Per cent. lactose=CX4Xl.llX1.05 

 volun f solution when the sugar is dissolved in 100 cc. 



A'. I! //'' The sampli-4 on arrival were immediately placed in glass-stoppered 

 bottl. - I 1 .. : ' removing portions for analysis they were rubbed down to a coarse 

 powder in a lur_'e porcelain mortar and mixed as well as possible. This was done 

 quite ruptdl), both toa\oid (xtteible changes in moisture content and to avoid forma- 

 tion of a p.c-ty maw. 



Crude liber First filtration was made on closely woven linen in a 4-inch Biichner 

 funnel \\iih liL-lit sueti..n. Second filtration was on a llcm U & A ashless filter paper 

 without .-net ion. lloth tiltratimis were rapid and satisfactory. 



lite are multiplied by the far tor 1.01 to correct for the dilution of 100 cc 

 of the M.lution by th- lllphuric arid. 



The method of Duboiswas followed exactly. It was necessary in extract- 

 ing \\ith uuterto break up \\ ith a u'la.-s rod the compact cake left after centrifuging the 

 la.-t time with 'ju.-olme. In \.-r-i--ns were made in the cold (50 cc-f-5 cc of hydro- 

 chloric acid, being allow. -.| to stand over night. All volumes were adjusted at 20 and 

 all poluri/.ution- \\ere made in jacketed tube at exact temperatures. The actual 

 pohiri-cop.- rea ragcs of four t<> five close readings) illustrate the very great 



influence that small ditTen-in .- in readinu's have upon the results, in these dilute 

 solution*, in .pit,- ,,f this fart, the method seems to be satisfactory and convenient 

 for judging milk chocolates. The methods are, in my opinion, in as simple a form as 

 possible, and can not well be improved. 



KM M\I\1KM>ATI()NS. 



In view of the Muall number of collaborators it is hardly possible for the referee 

 to make any formal recommendations based on collaborative work. It is evident, 

 however, that the Mudy of certain of these methods should be continued by the 

 aaaociatio: lly the cai'foin estimation and the determination of sugars in 



chocolate. There would appear to be no reason why the determination of extract in 

 tea as outlined by Doolittle and Woodruff should not be substituted for the cumber- 

 some Kraurh method. The experience of the referee on numerous samples of cocoa 

 products suggests that the requirement for filtering and weighing the crude fiber on a 



aj. Amer. Chem. Soc., 1907, 29: 556; see also Bui. 107, Rev., p. 256. 

 T.-.r,::; Hull. li 0!) 



