116 The Spraying of Plants. 



ALUM AND PYKETHRUM. 



Alum 2 ounces. 



Pyrethrum 3 large tablespoonfuls. 



Water 10 gallons. 



First dissolve the alum, after which the powder may be 

 added. This mixture has been recommended as possessing 

 special value in destroying cabbage worms. The applications 

 are made by means of a watering-can or sprayer when the 

 caterpillars are first seen. 



AMMONIA ; AQUA AMMONIA ; HARTSHORN ; VOLATILE AL- 

 KALI; NH 3 , THE GAS; NHJIO, DISSOLVED IN WATER. 

 Although ammonia alone possesses no practical value as an in- 

 secticide or as a fungicide, it is so frequently used in the prepa- 

 ration of the latter that it has interest in this connection. Am- 

 monia is the term popularly used to denote a solution of the 

 gas in water. It is a clear, colorless liquid, lighter than water, 

 and possessing an overpowering, pungent odor. It has a strong 

 alkaline reaction, and is a solvent of probably all the copper 

 compounds used in spraying. It is for this reason that the 

 article is of such importance in the preparation of certain 

 fungicides. Commercial ammonia varies greatly in strength, 

 but there are two methods of indicating its degree of concen- 

 tration. The older method is the one inaugurated by Beaume. 

 He used an instrument called a hydrometer, which showed the 

 specific gravity of liquids in accordance to an arbitrary scale 

 invented by himself. The following five items have been 

 selected from his table for testing liquids lighter than water. 



In the first column are degrees taken from his scale ; the 

 second shows the specific gravity (G.) of the liquid as compared 

 with water; the third shows the per cent of the weight of 

 ammonia gas (% Wt.) as found in the liquids which register 

 the indicated degrees upon the scale. The figures in the second 

 and third columns form the standards of measurement now 

 used by most chemists : 



Beaume, 16 indicates .960 G. or *9.8 % Wt. 

 " 20 " .936 " " 1(5.6 " 

 22 " .924 " " 20.4 " 

 i< 24 " .913 " " 24. " 

 " 20 " .901 " " 28.6 " 



