not generally used. Bottles with tight fitting corks of first quality 

 form the most satisfactory substitute. 



The preservatives most commonly employed for keeping compos- 

 ite samples are corrosive sublimate, bichromate of potash and for- 

 malin. The two former are sold in tablets prepared especially for 

 the purpose, and simply need to be powdered and dissolved in the 

 sample ; formalin (formaldehyde) is sold in 40 per cent, solutions 

 and the quantity needed for a composite can be easily added by 

 means of a small dropper or pipette. 



Corrosive sublimate tablets are to be preferred to other preserv- 

 atives as they interfere least with the action of the sulfuric acid in 

 making the test. Where the total solids of milk samples are to be 

 determined in addition to the percentage of fat, formalin can be 

 used to advantage as the amount necessary does not affect the accu- 

 racy of the test. Six to ten drops are sufficient to preserve a 

 pint sample several weeks if the sample is kept in a cool place. An 

 undue excess of any preservative should be avoided. 



A thorough preparation of the sample is of vital 

 Sampling and importance, and is best accomplished by gently 



Pipetting. rotating and by pouring back and forth from the 

 mixing vessel. Shaking and forcible pouring is not 

 permissable, as it is likely to cause partial churning and is sure to 

 inclose a large amount of air, rendering the sample unfit for pipet- 

 ting. All cream adhering to the sides and the stopper of the sample 

 bottle should be incorporated, and the resulting mixture not show 

 any solid particles of fat. A small, fine wire sieve is of great help 

 in detecting and correcting a lumpy condition. 



After mixing, the sample should be pipetted immediately as the fat 

 globules rise rapidly towards the surface. The pipette should be 

 first rinsed with the sample, then filled again slowly taking care to 

 avoid air bubbles, held in a vertical position when lowering the 

 liquid to the mark and read with the entire meniscus or crescent 

 above the line. In transferring to the test bottle, smearing of the 

 neck should be avoided as far as possible and the pipette blown 

 clear. 



Sour milk can be readily brought into a condition suitable for 

 pipetting by the use of a wire sieve to break the clots or by neutral- 

 izing the acidity with a small pinch of powdered caustic alkali or 5 



