218 THE CHEMICAL CONTROL OF THE DAIRY. 



34°, the specific gravity corrected to 60° F. is 32-9° = 1-0329 ; 

 or if tte temperature 'is 66° and the specific gravity 29°, the 

 corrected specific gravity is 29 '8° = 1 "0298. 



Never take the specific gravity of a milk without also 

 noting the temperature and correcting to 60° Fahrenheit. 



Instead of reading from the bottom of the curve and making 

 a mental allowance, the lactometers may be read from the top of 

 the curve and a definite figure (ascertained by a few carefully- 

 conducted experiments) added on. 



As soon as the specific gravity and temperature have been 

 taken, the corrected specific gravity from the table should be 

 entered in the book provided for the purpose of recording the 

 results. It is not necessary to enter the specific gravity in full, 

 but only the three significant figures ; thus a specific gravity of 

 1-0325 may be entered simply as 325 or 32-5. 



Though the determination of specific gravity has been de- 

 scribed first, it is found when total solids are to be estimated 

 that it is convenient in practice to proceed as soon as work is 

 commenced with their estimation, as this is an operation which 

 proceeds alone. Only in those cases where the sample is so 

 small that the lactometer will not conveniently float, if the 

 quantity necessary for total solid estimation has been removed, 

 is it usually convenient to take the specific gravity first. 



Estimation of Total Solids. 



A number of dishes or capsules, each marked with a separate 

 number and previously weighed, and a pipette marked to dis- 

 charge 5 grammes of milk of a specific gravity 1-032 at a tem- 

 perature of 60° F., are necessary. The dishes should be, if 

 possible, of platinum, and at least 1|^ inches internal diameter, 

 flat bottomed, and with a rim about ^ of an inch wide ; this rim 

 should be considerably wider at one side so as to form a lip on 

 which the number should be legibly stamped. These dishes 

 weigh about 12 grammes and cost £3 to £4 each. They may, 

 however, be replaced by porcelain dishes of about 2J inches 

 diameter, glazed all over ; these may be marked by scratching 

 the number on the side with a new file, painting this over with 

 a solution of platinum chloride, wiping ofi the excess, and igniting 

 the capsule ; the number will be marked in platinum. 



The dishes must be previously weighed on a balance accurate 

 to 1 milligramme, and the weights recorded on a table which 

 should be kept in the balance case. It has been found in practice 

 that, if the dishes be carefully cleaned, monthly weighings of 

 the dishes are sufficient, the average loss in this period for dishes 

 used daily having been found to be about 1 to 2 milligrammes. 



