1921.] 



Ag ri c ultub e A bbo a d . 



L168 



An interesting article on the firing of haystacks, by 

 G. Laupper, of Zurich, appears in the Swiss Agricultural 

 Yearbook for 1920. After a short historical 

 T e iring discussion the author gives a v< ry 

 ot Haystac s. exhaustive account of all the papers bear- 

 ing on the subject, and concludes his article with a useful 

 bibliography. In the light of the newer facts elucidated as a 

 result of recent research, the following account may be given 

 as to the probable causes of the firing of haystacks: — 



Four Phases in the Heating of Haystacks. — In the heating of 

 haystacks four successive phases may be distinguished. In 

 Phase 1. the hay sweats, and a temperature of 50°C. (122°F.) 

 is reached, generally within two days. The hay then passes 

 into Phase 2. Sweating increases, much vapour is given 

 off. together with an aromatic smell, and the hay becomes 

 a light brown colour. A temperature of 70°C. (158°F.) is 

 reached, usually in about a week. 



Phases 1 and 2 are considered desirable in the making of 

 hay. The heating in Phase 1 is due to the respiratory activity 

 of the plant cells; the heating in Phase 2 is variously attributed 

 by authors to bacterial action, ferment activity, and the 

 catalytic action of combinations of iron and manganese. The 

 exact cause of this heating is not yet clear, and further research 

 on the subject appears to be necessary, especially in view of 

 the importance of controlling this phase in order to prevent the 

 onset of Phases "3 and 4. 



In Phase 3 the temperature increases to 90°C. (194°F.), a 

 dark brown hay is produced, and much vapour is given off, 

 together with a pungent smell. The causes which lead to rise 

 of temperature in this and the succeeding phase are entirely 

 chemical in origin. A fortnight to three weeks may elapse from 

 the beginning to the end of Phase 3. 



Phase 4 culminates in combustion, and is a very dangerous 

 period. The temperature from 90°C. (194°F.) to ignition 

 point may be reached within two hours. The phase consists 

 of a damp distillation followed by dry distillation. Gases are 

 given off, a pungent and slightly burning smell may be detected 

 and the hay rapidly carbonises. Hay which has reached this 

 phase without eventually firing has a black-brown or black 

 colour, and has lost most of its nutritive value. 



It has also been shown that heating in the stack is most 

 liable to occur with young grasses containing a large propor- 

 tion of water-soluble material. In other words, the most 



