CULTIVATION WITHOUT OXYGEN. 187 



tube and the side arm, are then sealed in the flame. 1 

 This tube can be used for either solid or liquid media, 

 but, owing to its usual small capacity, gives better re- 

 sults with fluid media. (For precautions in using hydro- 

 gen see note to FrankeFs method, page 189.) 



Method of Buchner. The plan suggested by Buchuer 

 of allowing the cultures to develop in an atmosphere 

 robbed of its oxygen by pyrogallic acid gives very good 

 results. In this method the culture, which is either a 

 slant or stab culture in a test-tube, is placed tube, cot- 

 ton plug, and all into a larger tube in the bottom of 

 which has been deposited 1 gramme of pyrogallic acid 

 and 10 c.c. of -^ normal 2 caustic potash solution. The 

 larger tube is then tightly plugged with a rubber stopper. 

 The oxygen is quickly absorbed by the pyrogallic acid, 

 and the organisms develop in the remaining constituents 

 of the atmosphere, viz., nitrogen, a small amount of CO 2 , 

 and a trace of ammonia. 



Method of C. Frdnkel. Carl Frankel suggests the 

 following as a modification of, or substitute for the 



1 As the tubes come from the maker the contracted parts marked x in the 

 cut are usually so thick as to render the sealing in the flame during the pas- 

 sage of hydrogen somewhat troublesome ; it is better to draw them out in the 

 flame quite thin before passing the hydrogen into the tube. This makes the 

 final sealing a matter of no difficulty. 



2 A normal solution is one that contains in a litre as many grammes of the 

 dissolved substance as are indicated by its molecular equivalent. The equiva- 

 lent is that amount of a chemical compound which possesses the same chem- 

 ical value as does one atom of hydrogen. For example : One molecule of 

 hydrochloric acid (HC1) has a molecular weight and also an equivalent 

 weight of 36.5 ; a molecule of this acid has the same chemical value as one 

 atom of hydrogen. Its normal solution is therefore 36.5 grammes to the litre. 

 On the other hand, sulphuric acid (H 2 S0 4 ) contains in each molecule two re- 

 placeable hydrogen atoms ; its normal solution is not, therefore, 80 grammes 

 (its molecular weight) to the litre, but that amount which would be equiva- 

 lent chemically to one hydrogen atom, viz., 40 grammes (one-half its molecu- 

 lar weight) to the litre. A normal solution of caustic potash contains as 

 many grammes to the litre as the number of its molecular weight 56.1 

 grammes to the litre of water. 



