=Sulphur= can be used to advantage in the destruction of mold spores in cheese rooms, but the effect of the vapors of burning sulphur on germ life is relatively slight, unless there is an abundant supply of moisture in the air of the enclosed space, in which case sulphurous acid is formed which has a much greater effect. To have the desired effect sulphur should be burned at the rate of three pounds to each one thousand cubic feet of space, and the room kept sealed for at least twelve hours. If the sulphur is placed in an iron kettle which is set in a vessel of water, danger from fire will be avoided, and the heat generated by the burning sulphur will evaporate sufficient water to increase the effect of the fumes. =Formalin.= Another disinfectant that may be used as a liquid or as a gas is formalin, which is a watery solution of the gas, formaldehyde. It is much more powerful in its action than sulphur, and has a great advantage over corrosive sublimate and other strong disinfectants in that it is not so poisonous to animals as it is to bacteria and fungi. It can be used as a solution (one to five per cent) for the washing of woodwork, or for the treatment of any object, since it has no corrosive action. It can also be employed as a gaseous disinfectant for the treatment of rooms. It is most conveniently applied by suspending large cloths in the room and spraying them with the solution, then closing the room for a number of hours. =Bleaching powder.= Chloride of lime, or bleaching powder as it is often called, is a good disinfectant, as well as a deodorant. It is used as a wash in the proportion of four to six ounces to a gallon of water. It must be used with care in factories since the free chlorine that is given off has a penetrating odor. CHAPTER VI. PRESERVATION OF MILK. It has been shown in a previous chapter that milk becomes contaminated with a multitude of bacteria not only on the farm where it is produced, but during the various stages prior to its use. Many of the bacteria which find their way into milk are readily able to develop, and by their growth, render the milk unfit, or even harmful for human food. With the most stringent precautions that can reasonably be taken, it is impossible to avoid all contamination; hence, all grades of milk will soon spoil, unless some means of preservation is employed. Indeed, of all the foods classed as perishable, milk is the one that most rapidly deteriorates. Produced under ordinary conditions, it is unfit for ordinary use in a few hours if kept at 70° F.