SHIPS' BOTTOM PAINTS. In• general, the sub ject of painting the bottoms of iron ships may be divided into the preservation of the metal from corrosion and the prevention of fouling. The former is secured by applying any good anti-corrosive paint, and the problem, so far, is like the preservation of metallic structures in general. Sonic of the paint manufacturers at tempt to do this by a special paint ; others aim to make their anti-fouling compounds keep the water from the metal plates and serve both uses. The anti-fouling paints work by poisoning the organisms which attach themselves to the ship, and are chiefly of three kinds. One of these has for its active agent the oxides of copper; these were, in the first instance, ground and mixed with Stockholm tau•. The copper was supposed to dissolve slowly and to kill the adhering or ganisms. Its use was suggested by the successful use of copper sheathing on wooden ships, but the generally accepted theory. of the action of copper sheathing is that it acts, not by poison ing, but by a process of exfoliation or scaling oil'; that animals attach themselves to it, but that an outer layer of the copper peels oil and leaves a fresh surface. (See SIIEATIIING.) An other sort of copper paint is a copper soap. made by precipitating a solution of coalition soap with a solution of sonic salt of copper, thus making an oleate o• some similar salt of copper. This is a soapy or greasy substance, insoluble in water, and is applied hot, making a thick coating. This
is not a good foundation for animals or plants to attach themselves to, and it is cold inually wearing au-ay. The third, and at present the most numerous class of paints, are the varnish paints, already partly described, made from a spirit varnish. The pigment in these may be almost anything; commonly it is oxide of iron, sometimes with some white lead or white zinc; sometimes the coloring matter is Paris green, or some green pigment suggesting copper. The poisonous matter may be some arsenical com pound, but in some of the most successful ones it is a mercury compound. The arsenical com pounds are very cheap and are undoubtedly poisonous, but the mercury compounds are more intensely poisonous; that is, they poison with a less amount, but they are very expensive, costing for the most part about a dollar per pound of contained mercury. It may be doubted whether there is much choice among the mercury com pounds, as the sea water will convert any of them into corrosive suldimate. The essential thing seems to be to get a varnish which will last as long as possible, regard being had to the absolute necessity of having one which will dry almost immediately, then to put in enough mer cury or other poison to last as long as the var nish does, in quantity sufficient to kill everything with which it comes in contact.