254 HAYSTACKS 



The grass at this point had the composition 



Per cent. 



Proteids 9-13 



Ash 8-14 



Ether extract 3-24 



Woody tissue 31-36 



Non-nitrogenous extract . . . . . 48-13 



100-00 



It had a pleasant hay-like odour. Many moulds, bacteria and 

 micrococci were observed. The increase in the ether extract is at- 

 tributed to organic acids formed from the carbohydrates. 



No doubt such changes as above described take place during the 

 process of hay-making ; but usually they can only proceed to a very 

 limited extent, owing to the desiccation of the grass by sun and wind. 



When the partially dried grass is collected in stacks or barns, how- 

 ever, further desiccation is almost prevented, and the processes of 

 fermentation recommence. If the hay still contain much moisture 

 these processes proceed so rapidly that the very limited circulation of 

 air in the stack does not carry the heat away as fast as it is produced, 

 the temperature rises, fermentation is thereby favoured, and the tem- 

 perature gets higher and higher. 



While most organisms are killed by a temperature about 60, it 

 has been shown that certain bacteria, present in surface soil can work 

 energetically at 70 or higher. Eventually, however, even they will 

 be killed by the high temperature, and direct oxidation of some sub- 

 stances of the hay must then commence. 



A further exaltation of temperature then ensues until, under favour- 

 able conditions, the actual ignition point of the hay is reached and the 

 mass begins to inflame. Generally, however, the highest temperature 

 is reached near the centre of the stack, where access of air is difficult 

 and slow ; consequently a smouldering combustion rather than actual 

 flaming results. 



The conditions most favourable to the dangerous heating of hay- 

 stacks are not exactly known, but undoubtedly the presence of a 

 certain amount of moisture is one of the most important. Obviously, 

 then, one of the best methods of preventing the tiring of haystacks is 

 to thoroughly dry the hay before stacking it. This cannot always be 

 done, nor is it entirely satisfactory, for if over-dried, grass does not fer- 

 ment sufficiently to develop the aroma, flavour and colour which are 

 desirable in good hay. If hay has to be stacked while somewhat 

 green, one of two methods is generally adopted : 



(1) To mix salt with it. This probably acts by preventing or 

 hindering the growth of the micro-organisms. At the same time it 

 renders the hay more palatable and also probably lessens the risk of 

 its becoming mouldy. 



(2) To ventilate the stack. This is probably the more efficient 

 method. It is generally effected by including in the hay, at the time of 

 stacking, a sack or sacks filled with hay, placed vertically and drawn 

 upwards from time to time as the stack rises. Another method, often 

 employed in Scotland, is to erect, in the centre of the site chosen for 



