The possibilities of chlorine were early understood in connection with the bleaching of teeth, but the result was not satisfactory for the reason named, and also from the fact that no practical mode had been devised for its use. To present free chlorine to a tooth was an impossibility, owing to its irritating character and necessarily superficial action; and no plan had been originated to free it from its compounds, hence, all teeth suitable for bleaching were condemned to remain a perpetual disfigurement. The first attempt to present chlorine free to a tooth was made by Dr. James Truman, in 1862. Chlorine is liberated from chlorinated lime by all the acids, but more rapidly by some than by others. It was found that, as rapid action was not desirable, those acids that affected this were not satisfactory. Tartaric acid was one of these. The conclusion arrived at was that a 50 per cent. acetic acid was the best, although later investigation seems to indicate to the contrary. The difficulty attending the use of chlorinated lime is due to the fact that a good article is rarely to be found. Good chlorinated lime is in the form of a dry powder; when moist, it is worthless. It should have a strong odor of chlorine. A rough test can be made by adding to a solution of indigo, in a test tube, a small quantity of chlorinated lime; to this, add strong acid, and note the rapidity of change in color. If this is very slow, or not accomplished at all, the chlorinated lime is unfit for use, and should be discarded. INSTRUMENTS.—These, though very simple, require special notice, for neglect in this particular will involve total failure. _No iron or steel instruments should be used in any connection with the agent employed in bleaching._ This must be impressed on the mind of every operator. The reason for this is, that the salts of iron formed discolor the teeth very rapidly. It would be preferable not to use any steel instruments at any stage of the operation, but this is difficult to avoid in the excavation of the cavity. Instruments can be made of hard wood that will serve the purpose, but ivory, platinum or gold can be used in place of this—either of the latter materials making efficient instruments. Extreme care must be used not to produce any unnecessary irritation. The removal of all remains of decomposed pulp from the canal is of vital importance, but this must not be done in a rough, rapid, careless manner. It is of great importance that no inflammation of the periosteum should supervene, as that not only complicates the operation, but renders it more doubtful of success. The removal of the pulp should be followed by the usual treatment given to a tooth, and no attempt should be made to change the color of the tooth until all evidences of putrefaction have been removed, which will be manifested in the absence of the odor of decomposition.