Curing of Turki.sh Tobacco. 415 



Blistering- by the .sun, bruising, or allowing it to dry out too 

 rapidly will partly kill the tobacco and prevent the green colour from 

 disappearing, and no after-treatment will remove this. If the 

 tobacco has been harvested more or less ripe, and is allowed to remain 

 in the wilting-ioom for three or four days under favourable condi- 

 tions, even though the green colour does not disappear altogether, 

 this will be removed further in the drying oninp (curing- camp), and 

 subsequently in the bulk and bale during fermentation and ageing. 



The yellowiug* of the tobacco is dependent on the temperature and 

 humidity of the wilting-room. If the temperature is below 40° F. 

 practically no changes takes place, and should it be above 120° F. 

 then the cells of the leaves are killed too soon for the necessary 

 changes to take place. The most favourable temperature is between 

 60° F. and 100° F., but only provided the relative humidity is about 

 85 per cent. The amount of water-vapour in any given space depends 

 entirely upon the temperatuie. By raising the latter by 20° F. the 

 capacity of the air for holding water-vapour is doubled. Thus, by 

 raising the temperature in the wilting-room by 20° F. without the 

 addition of water, the relative amount of humidity is diminished by 

 50 per cent. On the other hand, if the temperature is lowered by 

 20° F., the relative humidity per cent, is doubled. In other 

 words, the capacity of a definite volume of warm air for holding 

 M'ater-vapour is greater than that of the same amount of cold air. 

 Hence, should the relative humidity be very great, and there is a 

 sudden drop in temperature, the atmosphere becomes saturated with 

 water-vapour, and moisture forms on the tobacco, which simply means 

 that the dew-point is reached.* 



In order to know whether the relative humidity is about 85 per 

 ct'Jit., a wet and dry bulb hygrometer is used. It consists of Im-o 

 precisely similar thermometers, mounted at a short distance from 

 each other, the bulb of one of them being covered with muslin, which 

 is kept moist by means of a cotton wick leading from a vessel of 

 water. The evaporation which takes place from the moistened bulb 

 produces a depression of temperature, so that this thermometer reads 

 lower than the other by an amount which increases with the dryness 

 of the air. 



* The air is at all limes more or less moist, and the degree of moisture is spoken of as 

 its hygroscopicity, and this is measured by instruments called hygrometers. As the amoimt 

 of water which can exist as vapour in a given volume of air is dependent upon its 

 temperature, by lowering the latter sufficiently, the moisture which existed as invisible 

 vapour is rendered visible in the form of dew. Tlie greater the amount of water vapour in 

 the air, the less is the amount of cooling required to form a deposit of dew, or the higher is 

 the dew-point. 



Tlie dryness or moisture of the air is related to the degree of its saturation with water 

 vapour, and not to the actual amount of water vapour present in it. Thus we may hare 

 air holding much vapour, but, from its warm temperature, capable of holding much more. 

 Such air feels and is drier, or more drying, than air holding far less moisture, but, due to its 

 coldness, is more nearlv saturated with all the vapour it is capable of holding at such a low 

 temperature. 



