FIXATION OF ATMOSPHERIC NITROGEN 393 



boilers, or of cargo like coal, which may undergo chemical change 

 and therefore possible spontaneous heating. 



When nitrocellulose commences to decompose from the 

 presence of minute traces of acid, a mixture of oxides of nitrogen 

 is given off among which nitrogen peroxide is recognisable 

 by its orange-brown colour. A test therefore is based on the 

 heating of the material in a long narrow test tube to 135 C. and 

 noting the lapse of time before the first faint yellow colour is 

 seen in the air contained in the tube. A more delicate test con- 

 sists in heating in a closed test tube a quantity of the cotton to 

 a prescribed temperature, while a piece of paper impregnated 

 with a mixture of starch with an iodide and moistened at the end 

 with glycerine is suspended in the tube. The number of minutes 

 which elapses before the paper becomes discoloured serves to 

 indicate the quality of the explosive according to its class. 



CHAPTER XXVII 



FIXATION OF ATMOSPHERIC NITROGEN 



AT the meeting of the British Association for the Advancement 

 of Science held at Bristol in 1898, Sir William Crookes in his 

 address as president drew attention to what he called the " Wheat 

 Problem." In the course of his discussion of the facts he produced 

 something approaching a serious sensation by the statement 

 that " England and all civilised nations stand in deadly peril of 

 not having enough to eat. As mouths multiply, food resources 

 dwindle. Land is a limited quantity, and the land that will 

 grow wheat is absolutely dependent on difficult and capricious 

 natural phenomena." 



It is true that he added to this alarming view, " I hope to point 

 a way out of the colossal dilemma. It is the chemist who must 

 come to the rescue of the threatened communities. It is through 

 the laboratory that starvation may ultimately be turned into 

 plenty." 



Fortunately for public peace of mind some relief from anxiety 

 was provided a few months later in a letter addressed to the 

 Times on December 2nd, 1898, by Sir John Bennett Lawes and 

 Sir J. Henry Gilbert, the famous experimental agriculturists of 

 Rothamsted, England. They said : " To sum up the world's 



