LARD AND LARD ADULTERATIONS. 511 



temperature not being allowed to fall below 95 C. to 100 C., constant 

 stirring at this part of the operation being most important. If the sa- 

 ponineation has beeu successful, the resultant soap is a smooth, thick 

 paste. Boiling distilled water is now added drop by drop, a thin, flexi- 

 ble spatula being used to break down the paste. When this has the 

 appearance of smooth starch, water may be run in till a volume of 500cc 

 is reached. Complete solution should follow. Forty cubic centimeters 

 of diluted sulphuric acid (1 10) are now added to the contents of the 

 basin, the liquid is stirred gently and brought to boil for seven to twelve 

 minutes, tken kept just below boiling, until the separated fatty acids 

 fuse to a clear oily layer. The greater bulk of the acid watery liquid is 

 siphoned off, the remainder with the fatty acids being poured into a 

 clean, warm flask With a somewhat long and narrow neck. The fatty 

 acids are freed as nearly as possible by siphouage from the watery 

 under layer, and the flask is filled up with boiling water so as to bring 

 the fatty acids into the neck, by which operation a partial washing is 

 given. Five cubic centimeters of the fused fatty acids are now trans- 

 ferred by means of a dry, warm, fast running pipette, into a clean, dry, 

 wide test tube. Twenty cubic centimeters of absolute alcohol are added, 

 care being taken to wash the pipette by running the alcohol through it. 

 The contents of the test tube are heated to incipient ebullition in a ves- 

 sel of boiling water. Two cubic centimeters of a 30 per cent, solution of 

 silver nitrate are now rapidly poured into the tube, when, if even 2 per 

 cent, of cotton oil be present in the sample, the characteristic cedar- 

 brown color is at once developed. Pure lard gives absolutely no 

 color. 



To quantify this reaction, known mixtures of pure lard and refined 

 cotton oil are treated exactly as above, and the colors in the different 

 tubes compared by reflected light against a white background. This 

 must be done simultaneously, for in about seven minutes the coloring 

 matter begins to fall out, and correct comparison is then impossible. 

 In careful hands excellent results are obtainable. 



Prof. J. Campbell Brown* calls attention to errors analysts are liable 

 to make : 



1. They are liable to underestimate the proportion of cotton oil when 

 relying upon the iodine test alone. The reason of this is found in the 

 admixture of stearine in adulterated lards which has a low iodine num- 

 ber. 



2. They are liable to condemn genuine lard which is more oily than 

 pork fat or lard rendered in England. According to Llehuer American 

 lard contains more olein than English. I do not think the assumption of 

 Helmer a just one since the iodine number of pure lards in this country 

 is found to be about the same as in England. 



Mr. Watson Greyt gives the results of some determinations of the 



*Op. cit.,p. 103. tOp. cit. 



