17 



mind when the water is added, the object being to add 

 the water at such a temperature that the temperature of 

 the fat at the close of the last whirling will be between 

 these two figures. 



The water used should preferably be soft water or con- 

 densed steam. The use of hard water is liable to cause 

 trouble on account of its carbonates; these are decomposed 

 by the acid, liberating carbon dioxid, which may cause 

 foam on the top of the fat column and obscure the menis- 

 cus. If soft water or condensed steam is not available, 

 hard water may be used if, before heating it, a few drops 

 of sulphuric acid are added. 



Reading the percentage. If the test has been successfully 

 conducted, the fat will be in a clear, yellowish liquid 

 column sharply separated from the clear and nearly color- 

 less acid solution immediately below it and with no foam 

 on top. The bottles should be kept warm either in the 

 tester or in warm water until read, and the readings should 

 always be made at between 130 and 140 F. The fat at 

 this temperature will, if other conditions have been cor- 

 rect, have a well-defined meniscus at both the top and the 

 bottom. The readings are made from the extreme bottom 

 of the lower meniscus to the extreme top of the upper men- 

 iscus. Figure 15 shows this graphically. An ordinary 

 pair of dividers is useful in making this reading. The 

 points are placed at the upper and lower limits, then 

 lowered until one point is at the mark; the other point 

 will indicate on the scale at the correct percentage for the 

 sample tested. 



In some steam testers where the exhaust steam escapes 

 into the jacket and no ventilation is provided, the tem- 

 perature of the bottles will be too high. In such case, the 

 bottles must be allowed to cool to 130 to 140 F. by plac- 

 ing them in water at that temperature for several minutes 

 before making the reading. 



Imperfect tests. If the foregoing directions have been 

 strictly followed, a perfect test should result. It is not to 

 be expected, however, that the beginner will always meet 

 with success. The next two paragraphs may be helpful in 

 locating the trouble. 



