42 MASS. EXPERIMENT STATION BULLETIN 339 



it has been processed, for instance while standing on the customer's doorstep, 

 then the whipping properties would be only slightly damaged. 



Studies under this project have been published as Bulletin 335 of the Massa- 

 chusetts Agricultural Experiment Station. 



The Effect of Aging Treatments on the Tyndall Phenomenon of 

 Gelatin-Water Solutions. (W. S. Mueller.) In this study on the effect of 

 temperature treatments on the light-scattering ability of gelatin sols and gels, 

 a need was felt for a tyndallmeter which would be extremely sensitive to changes 

 in light intensity, and would permit control of the temperature of the gelatin 

 while determinations were being made. After considerable preliminary ex- 

 perimental work, a photoelectric tyndallmeter was assembled in the dairy 

 laboratory. This instrument uses as its light-measuring elements two vacuum 

 photo-tubes, one of which measures the light transmitted from the solution under 

 observation while the other measures a fraction of the incident light after passing 

 through two Nicol prisms. The photo-tubes are electrically opposed and the 

 current is balanced by rotating the second Nicol prism. A sensitive galvanometer 

 is used as the indicating instrument. The relative intensity of the Tyndall cone 

 is measured in terms of angular degrees in which the Nicol prism must be 

 rotated in order to balance the photo-tubes. The angular degrees are converted 

 into relative light intensities. With this apparatus it is possible to observe the 

 intensity of the Tyndall cone throughout the aging period without disturbing 

 the gelatin solution cell. 



Among the advantages of the tyndallmeter here described are: Control of 

 temperature of the solution under observation; circumvention of moisture con- 

 densation on the solution cell when using temperature below that of room 

 temperature; a null measurement, indicated by a sensitive galvanometer; a 

 quickly established equilibrium; a negligible drift; and elimination of the 

 personal error which is encountered when comparing two similar intensities 

 of light with the eye. Furthermore, the instrument can be readily converted 

 into a turbidity meter. The chief disadvantages are that it is neither compact 

 nor portable. 



A detailed description of this instrument has been prepared for publication 

 and will be available for distribution in the near future. 



Observations with the photoelectric tyndallmeter during the past year con- 

 firm a previous report that a high initial (68° F. for 4 hours) aging temperature 

 increases the size or number of gelatin micellae. 



Nutritive Value of Chocolate-Flavored Milk. (W. S. Mueller, and W. 

 S. Ritchie, Department of Chemistry.) This study was undertaken with the 

 hope of demonstrating by animal feeding experiments whether the addition of 

 cocoa to milk changes the nutritive value of the milk. Also, it was hoped to 

 secure some data which might aid health officials in setting up standards for choco- 

 late milk. 



The effect of the addition of varying percentages of cocoa to mineralized 

 whole milk was studied by means of growth experiments on 72 albino rats. 

 When fluid chocolate milk containing more than one percent of cocoa was fed 

 ad libitum, the rate of consumption decreased as the percentage of cocoa in- 

 creased. When cocoa was added to whole milk powder and fed in controlled 

 amounts, the 1 percent cocoa diet was equal to the whole milk diet; the 2.5 

 percent cocoa diet gave a questionable retardation rate of growth; and the 4 

 percent cocoa diet definitely retarded growth. When the rats received the 7 and 1 

 percent cocoa diets, the feces in the intestinal tract were very hard and there 



