_Sodium Bisulphite._ | _Sodium Sulphite._ | 1. If in good condition it | 1. It has no perceptible has a powerful odour of | odour. sulphur dioxide.[9] | | 2. In solution it should turn | 2. In solution it should turn a blue litmus-paper red. | a red litmus-paper blue. | 3. It exhibits a marked tendency | 3. The tendency to "cake" to "cake" if the | is less marked than in drum is allowed to | the case of the bisulphite. remain open. | [9] High-grade sodium bisulphite has very little odour, but by the time it reaches the estate, and as a result of short exposure to the moist atmosphere of the tropics, a little decomposition sets in and a strong odour of sulphur dioxide gas is noticeable. It will be evident that, as sodium bisulphite under normal conditions gives off a gas when exposed to the atmosphere, it deteriorates in quality continuously. It is the potential presence of this gas which makes the powder effective as an anti-oxidant and disinfectant. It is within the experience of all accustomed to the handling of this chemical, that in addition to the loss of gas, the powder cakes into a hard mass on exposure. If only the top layer is caked, the remainder may be in fair condition; but no caked portions should be used, as they cannot be of good quality. They may, however, be used for the treatment of scrap rubber, to be discussed later. CARE OF SODIUM BISULPHITE.--The ready tendency of sodium bisulphite to deteriorate on exposure should give sufficient indication regarding its treatment in storage. It should be bought only in drums (or other air-tight containers), and should be stored in a dry place. No drum should be opened until required, and the common practice of keeping an open drum on the floor of the factory should be avoided. Drums are of two sizes, generally containing 1/4 or 1/2 cwt. respectively. It will be obvious that, although the prime cost may be cheaper with the larger quantity, it would always be preferable to secure the smaller drums, as the loss on exposure will be less. Most commonly the 56 lb. drum is purchased. It should not be difficult to calculate the period during which the contents will be consumed, on the basis of a maximum of 1 lb. per 100 gallons of latex. A 56 lb. drum, assuming no loss or waste, should be sufficient to treat _at least_ 5,600 gallons of latex (say, 8,500 lbs. of rubber)--if the bisulphite is of first-class quality, and the use is applied only to the preparation of fine pale crepe.