ANNUAL REPORT, 1931 213 



50° F. to 149° F., 68° F. gave the maxiinuin increase in gelatin efficiency. The 

 following results were obtained when mixes aged at 68° F. for 4 hours were com- 

 pared with mixes aged at the customary temperature (40° F.). 



1. Improvement in texture. 



2. Firmer body. 



3. Increased melting resistance. 



4. Slight reduction in overrun. 



5. Increase in basic viscosity and gel strength when 

 followed by a low aging temperature period. 



Increasing the gelatin concentration and also the strength of gelatin (Bloom 

 test) increased the magnitude of the high aging temperature effects. As would 

 be expected, the mixes with low total solids were found to be benefited more by 

 the use of a high aging temperature than were the mi.xes with high total solids. 



The use of a 68° F. initial aging period was found to be equivalent to approx- 

 imately 0.1 per cent gelatin. 



A check on the possibility of any increase in bacterial growth, titratable 

 acidity, or pH when the mix is aged at 68° F. for 4 hours showed no increase 

 which would be of any consequence in commercial ice cream manufacture. 



In an effort to ascertain the reasons for this behavior of gelatin, a thorough 

 study of the physical properties of gelatin is being made. A study of the optical 

 rotation of gelatin is now well under way. 



DEPARTMENT OF ENTOMOLOGY 

 A. L Bourne in Charge 



Investigation of Materials Which Promise Value in Insect Control. 



(A. I. Bourne). A recent development in the field of oil sprays is the appearance 

 on American markets of tar distillate oil emulsions which have been in general 

 use in Europe for several years. In Europe, these oils are products of the dis- 

 tillation of coal, lignite and, to some extent, wood; in America, much of the 

 material is obtained from coke ovens. Samples of both the English and the 

 American oils were used in the tests. These oils did not prove to be as satisfac- 

 tory indicators on trees in the orchard as are most of the common oil sprays; 

 consequently a tendency to overspray the trees was unavoidable. In dormant 

 application the English samples showed a slight tendency to retard the growi:h 

 of leaf and blossom buds; the American samples did not. When applied at late 

 dormant or delayed dormant stages of bud development, all of the oils caused 

 severe burning and, in many cases, outright killing of the buds. In these tests 

 the oils were not particularly effective in killing the overwintering eggs of the 

 European red mite, being considerably inferior to most of the common oil sprays. 



Tests with the typical American oil sprays included several new products 

 which have recently appeared on Massachusetts markets. Of these, Free Mul- 

 sion (Sherwin-\^'illiams Co.) and Oil-tone (Lucas Kil-Tone Co.) gave very satis- 

 factory results, particularly when used at a dilution of 5 gallons to 100. Kleenup 

 again gave a high degree of control. The red mite infestation was much heavier 

 in the college orchards than in 1930. This emphasized the necessity for a high 

 degree of control of the overwintering eggs, and strengthened the belief that in 

 combating a heavy infestation the stronger dilutions of oil emulsions are advisable. 



Of the miscible oils, Sunoco maintained its usual high degree of effectiveness. 

 Scalecide was somewhat less effective than in earlier tests. 



