a bottle which is placed inside another bottle, thus surrounding it with 

 an air jacket. This is set in a bath of cold water. The oil is constantly 

 stirred by a mechanical stirrer until it begins to thicken as shown by 

 the slowing down of the stirrer. Mr. Gladding would have the tempera- 

 ture lowered very slowly and make the determination in much the same 

 way as the titer of the fatty acids. He is, however, determining the 

 congealing point, which is not the determination made in the cold test 

 as ordinarily practiced, i. e., the melting point of the mixed oils, and 

 it is hardly to be expected that the congealing points and melting points 

 will be the same. 



In testing the lubricating oils, the oils should be dried, while in test- 

 ing salad oils where it is desired that the oils remain clear it is evident 

 that the water must not be removed. 



CLOUD TEST. 



The cloud test is given by Dr. Manns as follows: 



1. The oil must be perfectly dry, because the presence of moisture will produce 

 a turbidity before the clouding point is reached. 



2. The oil must be heated to 150 C over a free flame, immediately before 

 making the test. 



3. There must not be too much discrepancy between the temperature of the 

 bath and the clouding point of the oil. An oil that will cloud at the tempera- 

 ture of hydrant water should be tested in a bath of that temperature. An oil 

 that will cloud in a mixture of ice and water should be tested in such a bath. 

 An oil that will not cloud in a bath of ice and water must be tested in a bath of 

 salt, ice, and water. 



The test is conducted as follows: The oil is heated in a porcelain casserole 

 over a free flame to 150 C, stirring with the thermometer. As soon as it can 

 be done with safety, the oil is transferred to a 4-ounce oil bottle, Which must be 

 perfectly dry. One and one-half ounces of the oil is sufficient for the test. A 

 dry Fahrenheit thermometer is placed in the oil, and the bottle is then cooled by 

 immersion in a suitable bath. The oil is constantly stirred with the thermome- 

 ter, taking care not to remove the thermometer from the oil at any time during 

 the test, so as to avoid stirring air bubbles into the oil. The bottle is frequently 

 removed from the bath for a few moments. The oil must not be allowed to 

 chill on the sides and bottom of the bottle. This is effected by constant and 

 vigorous stirring with the thermometer. As soon as the first permanent cloud 

 shows in the body of the oil, the temperature at which this cloud occurs is noted. 



With care, results concordant to within 1 F can be obtained by this method. 

 The Fahrenheit thermometer is used merely because it has become customary to 

 report results in degrees Fahrenheit. 



The oil must be tested within a short time after heating to 150 C, and a 

 retest must always be preceded by a reheating to that temperature. The cloud 

 point should be approached as quickly as possible, yet not so fast that the oil is 

 frozen on the sides or bottom of the bottle before the cloud test is reached. 



This method seems to be entirely satisfactory except that the drying 

 would not be legitimate when the test is used on salad oils, as moisture 

 would affect the clearness of these oils as much as crystallized fats. If 

 the cloud test, as given by Dr. Manns, can be substituted in the testing 



