February, 1930] agricultural experiments 1929 1 1 



sulphuric acid, 2.2 per cent; copper sulphate in 10 per cent sodivun nitrate, 

 2.5 per cent; sodium bisulphate, 3.8 per cent; copper sulphate, 5 per cent; 

 iron sulphate, 15 per cent; ammonium sulphate, 20 per cent; and sodium 

 nitrate, over 20 per cent. 



The rate at which the herbicides dry, with one exception, did not ma- 

 terially affect their toxicity to mustard. The exception is iron sulphate 

 which is approximately twice as active when dried slowly. 



Since the toxicity of sodium nitrate and ammonium sulphate is 

 markedly affected by the temperature at which the sprayed plants are 

 grown, and iron sulphate varies in effect at different rates of drying, and 

 all these possess a low toxic value per unit of weight, their use as herbi- 

 cides seems undesirable. Of the remaining materials, if one assumes that 

 all substances having a toxic equivalent of 1 to 5 are equally desirable, a 

 selection may be based on relative cost, ease of handling, and corrosion of 

 spray machinery. 



The substances are not equally corrosive. A bright steel nail immersed 

 in the solutions at room temperature for six minutes showed on being 

 withdrawn a deep etching from the copper sulphate, a slight etching from 

 the sulphuric acid, and no visible effects from the copper nitrate, copper 

 sulphate, sodium bisulphate, and sodium bichromate. Four of the most 

 effective sprays have little or no action on iron. Copper nitrate, how- 

 ever, is too expensive, but copper sulphate and sodium nitrate mixed, 

 sodium bisulphate, and sodium bichromate are giving promise as very 

 desirable herbicides. {Hatch Fund.) 



MOSQUITO SURVEY MADE 



The white-marked salt-marsh mosquito is the worst of the five most 

 important mosquito species found on the New Hampshire seacoast by 

 P. R. Lowry. After the middle of July it became the dominant form out- 

 numbering all the other species combined, and remained until killed by 

 frost. 



Descriptions of this and 37 other varieties of mosquitoes found in New 

 Hampshire were published during the year in Bulletin 243, "Mosquitoes 

 of New Hampshire." Investigational work was conducted principally at 

 Rye and North Hampton. 



The greatest natural enemy of the salt-marsh mosquito is the killifish, 

 or mud minnow (Fundulus heteroclitus L.) In pools reached by the in- 

 coming tide it devours mosquito larvae and pupae before they can com- 

 plete their growth. {Hatch Fund.) 



EXPERIMENTS IN COOLING MILK 



When milk is cooled in the can by immersion in a refrigerated tank of 

 water the tank should contain approximately three to five gallons of water 

 to each one of milk being cooled, finds W. T. Ackerman in testing the 

 relative efficiency of various methods of cooling milk. Many tanks 

 are now deficient in this respect and cool too slowly. 



Pre-cooling by circulation of well water at 51 degrees Fahrenheit 

 through a tubular aerator will reduce the milk to a temperature as low as 

 52^ 2 degrees and has been accomplished at a cost of 25 cents for 100 quarts 



