526 Bulletin 281. 



Much more accurate results are obtained by heating the sample until 

 it is black. This is probably due to two factors : First, all of the moisture 

 is driven out of the sample; second, the apparatus becomes so heated 

 that some of the moisture which collects between the rubber stopper 

 and the flask is driven up into the graduated neck. The greatest care 

 must be exercised when the test is first started not to heat so rapidly 

 as to cause vapor to escape. 



The writer compared five sets of this apparatus with the gravimetric 

 method and found three of them to be made or calibrated incorrectly. 

 Of course this is no fault of the method. The fact that the apparatus 

 is made entirely of glass is an objection to its use in factories. In making 

 the test, it was found more convenient to balance the flask on the scales 

 and weigh out ten grams of the substance than it was to balance two 

 pieces of paper. It was somewhat difficult to put the paper and butter 

 into the flask without spilling some of the sample. It is of great import- 

 ance that the rubber cork exactly fit the neck of the fiask, as otherwise 

 moisture will collect at this point. After being used several times 

 the rubber stopper becomes cracked and collects moisture from the 

 sample. This difficulty may be partly overcome by thoroughly rubbing 

 the cork with the amyl reagent before each test. 



The advantages and disadvantages of the Gray moisture-test may be 

 summed up as follows: 



1. With proper manipulation and accurate apparatus, good results 

 may be obtained with the Gray moisture-test. 



2. The apparatus is fragile and not very durable. 



3. The chief sources of error in the Gray test are: 



(a) Danger in driving off moisture in the form of vapor from the 



upper end of the condensing tube; 



(b) Collection of moisture between the rubber stopper and the 



walls of the flask; 



(c) Cracking of the rubber stopper and the collection of moisture 



in the cracks; 



(d) Not heating the sample long enough. 



THE IRISH BUTTER MOISTURE-TEST 



This test was invented by A. H. Irish, of St. Paul, Minnesota. It 

 consists of a cup for holding the sample, weight for balancing the cup, 

 sample weight, percentage weights, hot pan lifter and forceps, a mirror 

 on which the moisture is condensed, and an alcohol lamp. Balances 

 are furnished with the test, but any accurate balance may be used. 

 A gas flame may be substituted for the alcohol lamp, but care must 

 be taken not to have the flame too high. 



