In taking down a lock the beginner should work slowly and cautiously, thinking in every case before acting. His screwdriver should be pressed well-down in the notch of every screw to prevent damage to the head, and if he apprehends the slightest danger of getting “things mixed,” he should lay each screw and its piece in different places upon his bench. Of course, there will be no such necessity after a few locks have been taken down, but such a necessity might exist at the very beginning; at least there is no harm to grow out of taking what is known to be the safe side in every case. The directions given for taking down, refer to the common lock, while locks of some of the modern guns will be made on plans quite different. But the principle will be the same, and hence there is no reasonable demand for going into further detail. The first object will be to get control of the mainspring so that it can be lifted out with ease. This attained, and all the rest of the work is easy enough. _To Clean and Oil the Lock._—Botches usually wipe the old oil and dirt from the parts with a rag, put on fresh oil, and then put the lock together again. This is a poor way, for a portion of the old gummy oil will be left to combine with the new, thus soon making it about as bad as the old. Every part should be thoroughly cleansed and dried before any new oil is used. First wipe the dirt and old oil off as thoroughly as possible with a piece of cloth or felt, and then rub it over with powdered chalk or Spanish whiting. Next brush off and rub with a stiff brush such as is used by jewelers or watchmakers. This will remove all the old oil, after which the new oil may be applied. Cases may turn up in which the lock has been long neglected, and the oil and dirt have gummed together so badly as not to admit of wiping off. In such cases the parts should be soaked for a short time in kerosene or in benzine, which is still better. This will dissolve the gum and render it easy of removal. In oiling, only oil enough should be applied to lubricate the parts—there is much more danger of getting on too much oil than too little. It should be put on with a stubbed camel’s hair brush or pencil, as the painters call it, and with extreme lightness. And there is but one kind of oil fit to be used on a lock, the very best “watchmaker’s oil” obtainable. Such an oil is comparatively costly, but a single bottle, costing 25 cents, will oil hundreds of locks, hence the cost is really not entitled to consideration, on account of its being so decidedly superior to any other oil in use.