MANURES AND MANURING I255 



The nitrate must have been lost in the course of this concentration and 

 determination. 



For the purpose of checking this loss, if any, the writer, with a soil 

 different from that previously used, made two mixtures with one kilogram 

 of earth with chrome leather under the conditions described. These two 

 mixtures were kept for fort}' days in two vessels ; at the same time, and 

 under the same external conditions, a kilogram of earth was studied b}'' way 

 of control. After 40 days, when the three lots were exhausted on the me- 

 thod used in the preceding experiments, the two liquids resulting from the 

 exhaustion of the mixture of earth and chrome leather were combined, 

 mixed and divided into two equal volumes. In one, after concentration, 

 the percentage was measured direct ; to the other there was added a quantity 

 of nitrate containing 0.150 gr. of nitric acid, it was then condensed and 

 the contents measured. The results arrived at were as follows : 



Nitric Acid per Kilogram of Earth. 



Existing in the soil at the start of the experiment 0.093 g^- 



Contained in the soil forty days later o.iio 



Contained in the mixture of soil and chrome leather .... 0.003 

 Found after the addition of 0.150 of nitric acid to the exhaust- 

 ing liquid 0.15=1 



The method of measuring the contents of nitric acid therefore -plays no 

 part in the results found. 



Agricultural Control. — 3 pots of equal size were used, each capable 

 of containing about 15 kg. of earth; into one, earth was put without manure, 

 into the second, earth mixed with chrome leather, and into the third earth 

 mixed with dissolved leather. In each pot 25 grains of wheat were sown 

 on the i6th April. These germinated normally on the 21st April. In the 

 early days of May the young wheat stalks differed clearly ; the plants grow- 

 ing in the pot containing earth mixed with chrome leather were of very poor 

 vitality, the leaves being j-ellowish in colour, while the plants in the other 

 pots were strong, and the leaves were a fine dark green, particularly in the 

 pot containing earth mixed with dissolved leather. The plants were weighed 

 on the 1st July. Taking the weight of the crop in the vessel to which no 

 leather was added as 100, the weight of the three crops will be represented 

 by the following figures : 



Earth without manure 100 



Earth ^\^th chrome leather 30 



Earth with dissolved leather 113 



Interpretation of the Results and Conclusions. — Chrome leather is inju- 

 rious to vegetation, and should therefore not be be regarded as a manure. 

 The chromium sesquioxide contained in this leather becomes hyperoxidised 

 in the soil, destroying the nitrates, and after five months' contact the decom- 

 position of the leather is so small that the earth with which it has been in- 

 corporated contains less nitrate than earth to which no manure has been 

 added. 



