CHEMICAL COMPOSITION OF AMERICAN GliAPES. 



11 



The methods of analysis followed are those laid down in Bulletin 

 No. 107, Kevised, Bureau of Chemistry; certain details for which no 

 explicit directions are given were made to conform to well settled 

 laboratory practice. Total solids were derived as for wine from the 

 table given in Bulletin No. 107, Revised (p. 218 et seq.), and the 

 sugar-free solids by subtracting the total reducing sugar from the 

 total solids, save in cases where the sample showed sucrose. In such 

 instances the sugar-free solids were obtained by subtracting the sum 

 of the reducing sugar and sucrose from the total solids. Subtracting 

 the total sugar found by inversion when sucrose is present results in 

 reducing the sugar-free solids below normal. 



The acid determination was made on filtered juice without previ- 

 ous heating, by titrating with tenth-normal sodium hydroxid, free 

 from carbonate, using a neutral solution of azolitmin on a spot plate 

 as indicator. When the juice was highly colored it was found 

 advantageous to dilute the portion taken about two and one-half 

 times with recently boiled but cold water, that the reaction might be 

 more clearly seen. 



The sugar determinations were made after the methods of Munson 

 and Walker (Bulletin No. 107, Revised, p. 241), but it was found pos- 

 sible to use the gooches twice without cleaning. This was definitely 

 determined by trial, as shown by the following check results: 



Reducing sugar determinations to test need of cleansing gooch before each determination. 



[Grams per 100 cc.J 



Filtered and weighed on clean pad: 



While grape juice 



1 21.11 



2 21.13 



3 21.11 



4.. . 21.11 



Average 21.12 



Red grape juice 



1 16.88 



2 16.87 



3 16.85 



4.. . 16.91 



Average 16. 



Filtered and weighed on 4.3 decigrams cu- 

 prous oxid: 

 White grape juice 



5 21.01 



6 21.05 



7 21.08 



8.. . 21.08 



Average 21. 06 



Red grape juice 



5 



6 



7 



8.. 



16.83 

 16.91 

 16.85 

 16.83 



Average 16. 86 



The Brix readings given are those made on the fresh juice, with a 

 standardized Brix must spindle especially devised by this laboratory 

 and corrected to 20 C. in accordance with the regulations of the 

 Bureau of Standards. The specific gravity readings given were in 

 every case determined by pyknometer when the sample was analyzed. 

 These notes apply to the work of 1909 and 1910; some slight varia- 

 tions from this detail occurred during the preliminary work of 1908. 



