XIX] VINEGARS 257 



20 COLOR.-TENTATIVE. 



Determine the depth of color in a Lovibond tintometer by good, reflected day- 

 light, using a ^ inch cell and the brewer's scale. Express the result in terms of 

 a -^ inch cell. 



FORMIC ACID. 



21 Fincke Method}. — Tentative. 



Employ the apparatus described under X, 39, Fig. 6. Introduce 100 cc. of the 

 sample into flask {A), add 0.4-0.5 gram of tartaric acid, and place in position as 

 shown in Fig. 6, the flask (JB) having previously been charged with a suspension of 

 15 grams of calcium carbonate in 100 cc. of water. Heat the contents of flasks (A) 

 and {B) to boiling and distil with steam from the generator (5), the vapor passing 

 first through the sample in flask {A), then through the boiling suspension of cal- 

 cium carbonate in flask {B), after which it is condensed and measured in the re- 

 ceiver (C). Maintain the volume of liquid in flask {B) as nearly constant as pos- 

 sible and reduce the volume of the sample in flask (A) to 30-40 cc. by heating with 

 small Bunsen flames, the distillation being continued until 1 liter of distillate is 

 collected. Disconnect the apparatus, filter the calcium carbonate suspension, and 

 wash the calcium carbonate that remains on the paper with a little hot water. 

 Render the filtrate faintly acid with hydrochloric acid, add 10-15 cc. of mercuric 

 chlorid reagent [ X, 38 (b) ], mix and heat on a boiling water bath for 2 hours. Filter 

 on a tared Gooch, wash the precipitate thoroughly with cold water and finally with 

 a little alcohol. Dry in a boiling water oven for 30 minutes, cool in a desiccator, 

 weigh, and calculate the weight of formic acid present by multiplying the weight 

 of the precipitate by 0.0975. 



22 ALCOHOL PRECIPITATE.— TENTATIVE. 



Evaporate 100 cc. of the vinegar to about 15 cc. When there is considerable 

 sugar in the vinegar, if the sample is evaporated to too low a volume, a gummy or 

 stringy precipitate is formed on adding the,alcohol instead of a flocculent one. When 

 the sugar content is high, therefore, the evaporation should not be carried beyond 

 20 cc. To this residue add slowly and with constant stirring 200 cc. of 95% alcohol 

 by volume and allow the mixture to stand overnight. From this point proceed 

 as directed under XIII, 18, beginning with the sentence, "Filter and wash with 

 80% alcohol by volume". 



23 PENTOSANS.-TENTATIVE. 



Proceed as directed in VIII, 84, except that 100 cc. of the vinegar and 43 cc. of 

 hydrochloric acid (sp. gr. 1.19) are used in beginning the distillation. 



TARTARIC ACID AND TARTRATES. 



24 Qualitative Test.— Tentative. 



Evaporate 50 cc. of the vinegar in a porcelain dish to a volume of about 10 cc, 

 filter into a test tube, add 1 cc. of 25% calcium chlorid solution and 2 cc. of 50% 

 ammonium acetate solution and allow to stand overnight. In the presence of tar- 

 taric acid a deposit of calcium tartrate is formed, the crystals of which may be 

 identified under the microscope by their characteristic form. 



25 TOTAL TARTARIC ACID.-TENTATIVE. 



Evaporate 200 cc. of the sample to a sirupy consistency to remove excess of acetic 

 acid, dilute to the original volume with water in a volumetric flask, determine the 



