Section 36(b) in The Indian Post Office Rules, 1933
(b)Great care shall be taken that the stopper or cork of the bottle fits tightly. This precaution is especially necessary when alcohol is used as a preservative; in such cases a ring of bee's wax or candle-wax shall be placed round the lip of the bottle so as to cover the shoulder of the stopper. The stopper shall be carefully fastened down with bladder or leather and sealed.
