THE MOJONNIER TEST 293 



(8) Be careful to pour off ether into dishes slowly at first 

 and gradually increase stream until full stream is running. 



(9) In using weighing pipettes make sure that neck of flask 

 is free from water when pipette is inserted. 



(10) Always use clean and dried pipettes. 



(11) If the samples for solids have to stand for any length 

 of time add the water just as soon as they are measured out, other- 

 wise there is a tendency to dry and a good mixture with the water 

 cannot be obtained. Keep dishes upon marble plate beside the bal- 

 ance, and not on hot plate support. 



(12) Redistill ether and petroleum ether, unless they are 

 known to be pure. This is unnecessary if these are bought from 

 a reliable firm. 



(13) Make sure that water is always running through cooling 

 plate. Watch pipe back of cooler. If tester is located in cold room 

 in winter add a gallon of denatured alcohol to tank to prevent 

 freezing. 



(14) Always aim to weigh empty dishes just before you are 

 ready to use them. It is not advisable to weigh them a long time 

 before they are used. 



(15) It is fundamentally important to see that weights are 

 read and posted rightly. Operator should keep his weights in syste- 

 matic, order upon balance pan. When a reading is taken it should 

 be checked at least three times. Learn to make weighings abso- 

 lutely right. 



(16) Every operator should from time to time have a sample 

 checked by a thoroughly reliable laboratory. 



// results on fat are high as compared with check results, the 

 cause may be one of the following : 



(a) Not keeping bottom of dishes flat. 



(b) Improper shaking and centrifuging shown by non-fatty 

 residue in dish. 



(c) Improper reagents (if in doubt run test upon reagents 

 substituting water for milk). 



(d) Temperature in fat oven too low. 



(e) Dirt has gotten into dish after ether was poured into it. 



(f) Improper reading or posting of weights. Weights have 

 lost weight from use. 



