(5) Setting the value of iodin solution by thiosulphate solution. At the time of adding 

 the iodin solution to the fat, two bottles of the same size as those used for the deter- 

 mination should be employed for conducting the operation described above, but with- 

 out the presence of any fat. In every other respect the performance of the blank 

 experiments should be just as described. These blank experiments must be made 

 each time the iodin solution is used. Great care must be taken that the temperature 

 of the solution does not change during the time of the operation, as acetic acid has 

 a very high coefficient of expansion, and a slight change of temperature makes an 

 appreciable difference in the strength of the solution. Example blank determina- 

 tions: (1) Forty cubic centimeters iodin solution required 62.05 cc of sodium thiosul- 

 phate solution. (2) Forty cubic centimeters iodin solution required 62.15 cc of 

 sodium thiosulphate solution. Mean, 62.1 cc. 



Per cent of iodin absorbed : 



Weight of fat taken grams. . 1. 0479 



Quantity of iodin solution used cubic centimeters. . 40. 



Thiosulphate equivalent to iodin used do 62. 1 



Thiosulphate equivalent to remaining iodin do 30. 2 



Thiosulphate equivalent to iodin absorbed do 31 . 9 



Per cent of iodin absorbed (31.9 X 0.012 X 100-*- 1.0479) 36. 53 



The following precautions should be exercised in the use of this solution: 



1. Great care must be used to prevent change of temperature of the solution, and 

 where any number of determinations are to be made blanks should be measured out 

 at short intervals. This precaution applies as well to the use of the Hiibl solution, 

 as the coefficient of the expansion of alcohol is large. 



2. When the potassium iodid is added the solution should be thoroughly mixed 

 before the addition of water. 



3. The acetic acid must be full strength and pure in order to obtain a solution 

 which will keep well. 



[Note by Editor. In this connection it is suggested that the Hiibl 

 and Hanus methods should be rewritten and combined where possible, 

 as they are identical in many respects, and the inclusion of the full 

 text of both in the methods is unnecessary.] 



The method for the titer test was adopted as a provisional method. 

 (See Circular 27, Bureau of Chemistry, for the full text of this method.) 



ERRATUM. 



On page 24, last column, fifth figure from the end, change " 1,4468" 

 to "1,4:768." 



III. DAIRY PRODUCTS. 



Twentieth. Convention, 1903, Bui. 81, Cir. 13. 



On page 36, under "6. Detection of Formaldehyde," designate the 

 method there given as " (a) Hehner's method," and insert the follow- 

 ing as a provisional method: 



(b) THE HYDROCHLORIC ACID AND FERRIC CHLORID METHOD. 



Aim. Kept. Mass. State Board of Health, 1897, p. 558; Food and Drug Reprint, p. 20. 

 To 10 cc of milk in a porcelain casserole add an equal volume of concentrated 

 hydrochloric acid containing 1 cc of 10 per cent ferric chlorid solution to each 500 cc 



