June 25, 1909] 



SCIENCE 



1009 



(2.5 grs. of azolitmin in 100 c.c. water) diluted 

 one to five thousand — one or two drops of deci- 

 normal potassium hydrate was added to each 

 Nessler's tube to bring out the color. From this 

 comparison the number of grams required to make 

 one thousand cubic centimeters of a standard was 

 interpreted. 

 Variation in the Acidity of Fresh Milk: W. M. 



EsTEN, Storrs Agricultural Experiment Station, 



Storrs, Conn. 



The extreme variation, of a herd of 26 cows, 

 covering a period of seven months, was from .075 

 to .23 per cent. The samples of milk were taken 

 about every fortnight. The method of testing the 

 acidity was by titration with iV normal NaOH, 

 using 17.6 c.c. of milk and dividing the amount 

 of tenth normal by 20. This result gives the 

 per cent, of acidity in terms of the lactic acid 

 molecule. The samples of milk were collected 

 from each cow in the morning from 5 to 6 and 

 were titrated about 10 a.m. In the interval, after 

 a vigorous shaking, 2 c.c. of milk were taken 

 from each sample for the bacteriological test. 

 The experiments commenced on May 16 and ex- 

 tended to December 16. When curves were plotted 

 and drawn for each cow, for diflferent breeds of 

 cows, for averages of breeds and for all the cows 

 collectively, it was discovered that individual 

 cows varied in their own curve and from the 

 curves of the other cows, and that the breeds 

 markedly varied from one another. There was 

 also indicated for every cow a marked decrease 

 in acidity during the summer, and a marked in- 

 crease during the winter months. The food and 

 seasonal period seemed to be controlling factors 

 in the variation. The eleven Jerseys had an aver- 

 age acidity of .18 per cent., while the Holsteins 

 had an average acidity of .16 per cent. The indi- 

 vidual Jerseys showed a larger variation than the 

 individual Holsteins, indicating that the Jerseys 

 are more susceptible to changes and have a more 

 sensitive nervous temperament. The total average 

 of 378 tests on 25 cows was precisely .17 per cent., 

 a value which gives a fairly correct idea of the 

 normal acidity of milk. 



Some of the most marked variations in acidity 

 were found among the Jerseys and one Guernsey. 

 One Jersey had an acidity of .13 per cent, at the 

 close of her lactation period and commenced the 

 next with an acidity of .2275 per cent. Three 

 other Jersey cows had acidities of .22, .225 and 

 .23, respectively, as their highest extremes. These 

 cows were apparently in perfect health. It was 

 found that pathological conditions had an effect 



on the variation of acidity instanced during the 

 summer by a cow with a sore foot. This cow's 

 milk showed a drop to .125 on July 8, a rise to 

 .18 on July 27 and a drop to .135 on August 7. 

 After her recovery her milk acidity rose to .19 

 and varied afterwards but little. All these results 

 lead to the conclusion that certain factors of food, 

 conditions of health and the change of seasons 

 have their effects, which are shown in the changes 

 of acidity in the milk. A Guernsey had the most 

 remarkable variation of all. Her average was 

 only .108 with variations from .075 to .13. This 

 is the lowest extreme in acidity that has, to the 

 writer's knowledge, been recorded. 



The question arises. What are the neutraliza- 

 tion elements which we call acidity of milk? Is 

 it the easeinogen alone, or easeinogen combined 

 with other compounds, that causes the reactions? 

 It has been silggested that the amount of acidity 

 is an indirect indicator of the amount of easein- 

 ogen present. If this be true the acidity test 

 would be a simple and rapid determination for 

 the approximate amount of easeinogen present. 

 It is to the chemist that we must submit the 

 problem for solution. 

 Cost of Heating an Incubator tctith Electricity: 



W. M. EsTEN, Storrs Agricultural Experiment 



Station, Storrs, Conn. 



There are two important factors which deter- 

 mine the economic application of electricity in the 

 heating of incubators for constant temperatures, 

 namely, the insulation and the heating and regu- 

 lation devices. 



Copper is universally used in constructing in- 

 cubators for laboratory use. With the exception 

 of silver, copper is the best conductor of heat 

 known. The insulating material used with copper 

 is imperfect and not properly applied for prevent- 

 ing loss of heat. Copper incubators are generally 

 water-jacketed and leaks often arise, causing dis- 

 agreeable annoyances. The duration of the copper 

 is somewhat limited. If such materials as as- 

 bestos, hair felt, wood and cork board are selected 

 and used in combination there can be constructed 

 an incubator, fire proof, with almost perfect in- 

 sulation, and practically indestructible, at about 

 one quarter the cost of a copper incubator. More- 

 over, the diminished cost of operation will pay 

 for its construction cost in a few years. The 

 writer has constructed one of these incubators out 

 of asbestos, wood, hair felt and building paper 

 with an inside capacity of three and a half cubic 

 feet, which costs less than one dollar a year to 

 heat to a constant temperature of 37° C. 



