TECHNIC BACTERIOLOGICAL EXAMINATION OF SOILS. 275 



Dilution and Test Bottles. 



Whitall-Tatum Co's make, (Figure I — regular shape, saltmoutii bottles 

 have been found more satisfactory for making dilutions and soil extracts 

 than erlenmeyer flasks. The sizes used are 8, 12 and 16 ounces respectively. 

 The 8 and 12 ounce sizes being used in making dilutions and the 16 ounce 

 size for extracting nitrates. The advantages of these bottles for making 

 dilutions are that they stand sterilization at 200° C, can be compactly piled 

 into the hot air sterilizer, are not as easily broken as flasks, and can be ad- 

 vantageously washed with a bottle brush. (The bottle breakage with us has 

 been about one tenth what the erlenmeyer flask breakage used to be, and the 

 bottles apparently stand sterilization as well.) 



Container for Sterilizing and Keeping Sterile Water. 



All water is sterilized by boiling on three successive days in an especially 

 constructed copper boiler, lined with tin. Figure II. The boiler is an 8 gallon 

 copper aspirator bottle having a rather large and long neck, allowing first, 

 a large cotton plug (which permits the water to be boiled without blowing 

 out the plug), second, the transmission of enough heat to thoroughly dry 

 the cotton plug after boiling is over. The outlet tube is closed by a rubber 

 stopper, through which passes a tube fitted with a glass stop-cock. The 

 glass tube on the other side of the stop-cock contains a right angle bend. 

 The stop-cock and outlet tube are sterilized by allowing about a pint of boil- 

 ing water to run out through them each time the water is boiled, and kept 

 sterile by keeping the end of the tube immersed in a test tube of 70 percent 

 alcohol, or 3 per cent hydrogen peroxide. 



For Incubation Tests. 



One half pint jell glasses with loose fitting lids are used as containers for 

 soil subjected to incubation tests. The jell glass is preferable to either a 

 beaker or tumbler because it has a lid, and is to be preferred to a beaker be- 

 cause the soil can be removed by inverting the jell glass and dropping it with 

 smart slap, on a hard surface. 



Pipettes. 



The short form volumetric pipettes, Figure III, are used for making 

 dilutions and in taking aliquots for plating. These can be used as accurately 

 as the regular form and apparently have the following advantages for bac- 

 teriological work: (1) are easier to handle and wash; (2) can be readily 

 sterilized in large test tubes, as they pack in well and are not as liable to 

 breakage; (3) are easier to fill; and (4) soil emulsions drain out more quickly 

 and completely from them. 



