PIPETTES, FLASKS, GEEBER BOTTLES. 



TABLE CXXIX. — Calibration of Bcjkette. 



413 



III. Pipettes. — Pipettes are used for measuring liquicl.s by filling tlit-ra 

 to tlie mark and letting the liquid run out; the following points should 

 be noticed : — 



(a) The bottom of the meniscus should coincide -n-ith the mark. 



(6) The pipette should be held vertically while it is running out. 



(c) The liquid should always be allowed t(j run out in the same manner. 



Perhaps the best manner of allowing tlie liquid to run out is to allow it 

 to flow as fast as possible, and, wlicn emptj-, to touch the surface of the 

 liquid with the point and to withdraw it at once. It may, hu\\c\er, be 

 allowed to run out slowly, or a definite number of droiis maj- be permitted 

 to run out after the main portion is dclivoicd. \Vhatever mctliod is- 

 adopted during graduation must be strictly ailhcicd to in practice. 



The graduation of pipettes is very simple ; they arc filled with water 

 as near 60° F. (15-5° C.) as possible, the contents run into a weighing 

 bottle and the water weighed. 



The pipettes should lie each etched with a number and the weight of 

 water delivered tabulated for use. 



I'ipettes used exclusively for delivering known weights of milk should 

 be gi-aduated with milk of l(y^'2 specific gravity containing fioni 3-.) to 

 4-0 per cent. fat. In tliis case, the reading should be from the top of the 

 meniscus, as the lower edge is invisible. 



IV. Flasks. — Flasks of capacity sufficiently,- small to permit of lieing 

 weighed when full, are filled vi-ith water as near 00° F. as possible, and 

 Meighed. Each should be marked with a ninuber, and the weight of water 

 contained by each tabulated. 



Larger flasks (c.;/., litre flasks), if no balance sufticientlj- large is available, 

 are graduated by the following method : — 10 successive portions of a little 

 less than 100 grammes of water at about G0° F. (15-5° C. ) are weighed into 

 the flask (best from a 100 c.c. flask). A )icaker containing a little water, 

 and a pipette are now weighed, and the litre flask filled to the mark by 

 water from the pipette ; the beaker, pipette, and remaining water are now 

 weighed ; the difference between the weights and the total weight of the 

 ten portions added together will give the weight of water in the litre flask. 



V. Lefflnann-Beam op GerbeP Bottles.— These can be graduated 

 with sufficient accuracy bj' using each to make determinations of fat in 

 several samples of milk, in which the fat has been care&dly estimated )>y a 

 good gravimetric method (e.^., the Adams method). Those bottles which 

 show a marked difference (« C, more than 1 per cent.) should be rejected. 



The scale should also be measured with a finely-divided rule, and any 

 bottles showing marked irregularities of graduation must be likewise 

 rejected. 



