May 22, 1914] 



SCIENCE 



765 



fying power which varies with the type of soil, soil 

 treatment, etc. 



The sulfofying power of soils may be deter- 

 mined in the laboratory in the following way: 



100 grams of fresh soil obtained with all pre- 

 cautions that it shall be representative and uncon- 

 taminated are weighed out in tumblers and thor- 

 oughly stirred. Then 0.1 gm. of a sulfide (Na.^S) 

 or sulfur is added. Moisture conditions are brought 

 up to the optimum by additions of sterile water. 

 The soils are incubated for 4^5 days at room tem- 

 perature. At the end of that time the sulfates are 

 leached out by shaking for six hours with water in 

 a shaking machine. The sulfate content of the soil 

 itself is determined and the purely chemical oxida- 

 tion, of the sulfide occurring upon shaking the sul- 

 fide for six houis with the soil is also ascertained. 



The sum of these two is subtracted from the 

 total sulfate content of the soil after incubation 

 and the difference gives the sulfofying power of 

 the soil, or the physiological efficiency of the sul- 

 fuToxidizing bacteria in the soil. Many difficulties 

 have been met in the work and largely overcome. 

 Details regarding these will appear in a future 

 publication. The point to be emphasized by the re- 

 sults so far is that soils have a definite sulfofying 

 power which is determinable in the laboratory and 

 therefore the efficiency of fertilization of soils with 

 organic sulfur compounds may be ascertained for 

 any soil. 

 Further Studies with Some Azotoiactcr : Dan H. 



Jones. 



Viability of Azotoiaoter in Steele Cnltxires. — 

 Equal quantities of azotobaeter growth were taken 

 from cultures grown on Ashby's agar for varying 

 periods of time and plated out in beef gelatin. 

 The relative colony counts were as follows: 



Culture 16 days old 9,000 colonies 



Culture 2 months old 8,000 colonies 



Culture 5 months old 5,000 colonies 



Culture 7 months old 4,500 colonies 



Culture 1 year and 4 months old . . . 2,200 colonies 



Culture 2 years and 2 months old . . 60 colonies 



This work was duplicated with the four varieties 

 of azotobaeter under observation with approxi- 

 mately same results. 



Thermal Death Faint of Azotobaeter in Stock 

 Cultures of Different Ages. — The cultures used for 

 the viability test were tested for their thermal 

 death point, by mixing one loopful of culture in 

 10 c.c. of Ashby's solution and then held in water 

 bath for 10 minutes at the required temperature. 



All cultures heated up to 55° C. gave good 

 growth. 



All cultures heated up to 65° C. and over gave 

 no growth. 



Involution Forms. — Involution forms of azoto- 

 baeter varying very much in shape and size may 

 appear in cultures grown in Ashby's solution and 

 Ashby's agar at any temperature within growth 

 limits. This tendency to produce involution forms 

 is comparatively slight at 20°-25° C, but excessive 

 at 37° C. Involution forms taken from an Ashby 

 agar culture 2 months old were tested for their 

 power to reproduce in Ashby's agar in moist cham- 

 bers. Fifteen were held under observation for 

 four days, but during that time only one repro- 

 duced. Normal cells present in the same fields 

 produced colonies which overgrew the involution 

 forms. 



Azotobaeter and Plant Growth. — It was decided 

 to test the power of azotobaeter to fix sufficient 

 atmospheric nitrogen for plant growth. Special 

 vessels were designed for the purpose. These were 

 filled with well-washed quartz sand, sterilized, 

 soaked with Ashby's solution and inoculated with 

 azotobaeter, controls being kept. After two 

 weeks, grains of wheat were sotiti in the pots of 

 sand. These all germinated and gave growth-pro- 

 ducing plants 16 inches high in one month, but no 

 difference was observed at this time between the 

 culture plants and the controls. 



A Possible Improvement in the Technique of De- 

 termination of the Ammonifying Power of Smls: 

 T. D. Beckvtith and A. P. Vass. 

 One of the difficulties met with in determining 

 the ammonifying power of soils is that part of the 

 ammonia was lost under the older methods. We 

 have found it possible to determine the total 

 amount of ammonia given off by soils by a very 

 simple method of laboratory technique. The soil, 

 generally 100 or 200 grams in content, is placed in 

 a 1,000 c.c. Erlenmeyer flask. In the top of the 

 flask is inserted a two -hole rubber stopper. The 

 air is allowed to enter the flask through the in- 

 verted U-tube. The outer tube is made of a simple 

 elbow placed in the other hole of the stopper. 

 This flask thus prepared is connected with a water 

 pressure filter pump. In the series between the 

 soil flask and the pump is placed a wash bottle 

 containing iV/10 H-So.,. For purposes of an indi- 

 cator this acid solution is colored slightly with 

 cochineal. When soil and the material to be am- 

 monified is placed in the soil flask, air is drawn 

 through the system by the filter pump. The am- 

 monia is intercepted by the acid. The indicator in 

 the wash bottle shows the point of neutralization. 



