212 THE CHEMICAL CONTROL OF THE DAIEY. 



handling a churn of milk — i.e., straining and transferring to the 

 vessel in which it is sent away from the dairy — is about 35 seconds, 

 and the quickest analysis, other than the taking of the specific 

 gravity, occupies at least two minutes ; so that to test each churn 

 in this way would mean delaying the handling of the milk to 

 an extent which is incompatible with the proper working of 

 the dairy. The testing of the milk in the laboratory that has 

 passed the specific gravity test must, therefore, be done after 

 the milk has been disposed of. It has been found that it is not 

 necessary in this case to test the milk in every churn^ as the 

 results are for guidance as to the quality of milk that may be 

 expected from difierent sources, and one sample per day from 

 each farm is sufficient for this ; the morning and evening meal 

 should be sampled alternatively. If adulteration is detected, or 

 if the milk is of abnormal quality, the whole of the churns from 

 that particular farm should be tested. It is also desirable to 

 test the whole of the churns from each farm at intervals, say once 

 a month, in order to see that the difierence between them is not 

 excessive. No strict rule can be laid down for the taking of 

 samples ; the chemist must use his discretion, based on experi- 

 ence, as to what samples he will have taken. 



Analysis of the Samples. — The cans should be brought at 

 once to the laboratory and the lid of the tray opened ; the 

 samples are then to be arranged in alphabetical or numerical 

 order, or in any wa,y that may be most convenient ; a methodical 

 system in this respect will be found to minimise any chance of 

 error in dealing with large numbers of samples. The procedure 

 must vary in difierent dairies ; if the samples are very few, the 

 samples taken at difierent times of the day may be left till a 

 suflicient number have accumulated and all examined at once. 

 In this case, it is necessary to preserve them in a cool place, 

 especially in summer ; but where the time can be found it is 

 preferable to make two or three series of analyses a day. An 

 examination of the lids of the cans should be made to see if any 

 of the milk has been splashed upon them, and if it is not possible 

 to obtain a new sample the portion adhering to the lid should be 

 washed down into the can with some of the sample. The analysis 

 should comprise the following data : — Specific gravity, fatj and 

 total solids, and (by difierence) solids not fat. The specific 

 gravity should be estimated by means of a lactometer. The 

 fat may be estimated by the Leffmann-Beam or similar methods, 

 or may be calculated from the total solids and specific gravity. 

 The total solids may be estimated by evaporation, or may be 

 calculated from the fat and specific gravity, The choice of 

 how the analysis is to be conducted will depend upon the time 

 available. The most reliable mode of work is to estimate both 



