160 PKO VISIONAL METHODS FOB ANALYSIS OF FOODS. 



It may be mentioned that the temperature has practically no influence on the 

 readings. Edgar B. Kenrick, University of Toronto; Frank B. Kenrick, University of 

 Manitoba. 



Page 106, 12, (b). Has anyone ascertained how accurately a mixed precipitate of 

 ferric and aluminum phosphates can be calculated into its components from its gross 

 weight and (Al PO 4 =122; FePO 4 =151; P 2 O 5 = 142 ) total phosphoric acid? 

 Let x and ?/=Al P0 4 and Fe P0 4 , respectively; then x-\-y=a\ 



. 142*' , 142 y 

 and ~24T+W^ 6 - 



Page 107, 12, (d). Would you not usually recommend the indirect calculation of K 

 from the weight of mixed chlorids and total chlorin as being much less laborious 

 than the precipitate of K 2 Pt C1 5 ? A. Me Gill. 



FOOD PRESERVATIVES. 



Page 108, 3. It would be well to note that chloroform is much more convenient 

 than ether for these extractions. 



A more convenient way to apply the ferric chlorid test is to use a portion of the 

 chloroform solution without evaporation. Shake this portion in a small test tube 

 with about 1 cc of water, and add a very small drop of weak ferric chlorid solution; 

 the violet color will be observed in the aqueous layer above the chloroform if 

 salicylic acid is present. Successive small drops of ferric chlorid should be added 

 until the deepest color is obtained or until it is evident that salicylic acid is not 

 present. An excess of ferric chlorid must be avoided, as it tends to destroy the 

 color; but, on the other hand, if the first addition of ferric chlorid does not produce 

 the reaction, enough must be added to make sure that the color can not be obtained. 



Page 109, 4. The oxidation method devised by the writer (see Bulletin No. 59, 

 TJ. S. Department of Agriculture, Division of Chemistry, page60;orLeffmann's Select 

 Methods in Food Analysis, 1901, page 98), based upon the oxidation of benzoic 

 into salicylic acid (Hanriot, C. R. 102, page 1250), has been in use in this laboratory 

 for nearly three years with good results, and I think it worthy a place in our 

 methods. Recently Mr. J. O. LeBach, food chemist of this station, has simplified 

 the manipulation by doing away with the cooling in ice water and performing the 

 oxidation in a test tube instead of a dish. Mr. LeBach describes his method of 

 making the test as follows: 



Transfer about 0.05 gram to 0.1 gram of the dry residue from the chloroform or 

 ether extract of the suspected sample to a test tube holding about 50 cc; add from 

 5 cc to 8 cc of concentrated H 2 S0 4 , shake until the mass is dissolved, then add from 0.5 

 to 0.8 gram of barium peroxid, a little at a time, shaking and cooling in water after 

 each addition of the peroxid. After all the barium peroxid has been added a per- 

 manent froth should have been formed on the sulphuric acid. Let stand from 20 to 

 30 minutes, then fill the test tube three-fourths full of water, shake and cool rapidly 

 to the temperature of the room. Filter off the barium sulphate and extract the 

 filtrate with chloroform or ether. Draw off the chloroform and test it for salicylic 

 acid in the usual way with dilute ferric chlorid. 



It is important that during the oxidation of benzoic acid to salicylic acid with 

 barium peroxid the temperature of the solution should not go higher than ordinary 

 temperature; the cooler the better. 



I have been able to oxidize benzoic acid to salicylic acid with commercial hydrogen 

 peroxid, but have not found the method as easy to control as the one given above. 

 Ammonium persulphate works as well in most cases, but sometimes fails to act 

 properly. With barium peroxid I have never had a failure. 



We find that saccharin, when oxidized in this manner, gives the salicylic acid re- 

 action. It is therefore necessary, before applying this test, to determine by the taste 

 whether saccharin is present. Of course it is necessary also first to prove the 

 absence of salicylic acid. Alfred M. Peter, 



