In the thermo-regulators which have been constructed heretofore, the heat has been regulated by the variation in the inflow of gas to the heating flame. The apparatus described below, and shown in the accompanying cut, taken from the _Zeitschrift fur Instrumentenkunde_, operates on an entirely different principle. The distillation and condensation process of a fluid heated to the boiling point in the vessel, A, is as follows: [Illustration] The steam passes first through the pipes, _a_ and _c_, into the serpentine tube, where it is condensed, and then flows through the tubes, _d_ and _b_, back into the vessel, A, if the cock, _r_, is closed, but if the said cock is open, it flows into the receptacle, K. When the liquid begins to boil the steam passes freely through the tubes, _d_ and _b_, part passing through the tube, _f_, out into the air, and the other part passing through the open cock, _r_, to the receptacle, K; but the condensed liquid soon closes these passages to the steam. At _h_ is an opening for a thermometer, _t_, and through this opening the liquid can be poured into the vessel, A. If the cock, _r_, is kept closed, the volume of liquid in the vessel, A, cannot be diminished, and the bath, B, must take the constant and uniform temperature of the steam in the vessel, A, as the vessel, B, is heated evenly on all sides. This apparatus can also be used as an air bath, in which case the vessel, B, is left empty and closed by a suitable stopper. * * * * * PIPETTE FOR TAKING THE DENSITY OF LIQUIDS. The accompanying engraving represents a simple apparatus, which any person accustomed to working glass can make for himself, and which permits of quickly, and with close approximation, estimating the density of a liquid. In addition, it has the advantage of requiring but a very small quantity of the liquid. It consists simply of a straight pipette, A B, to which is affixed laterally, at the upper part, a small U-shaped water gauge. The two branches of the gauge, as well as the pipette itself, are graduated into equal divisions. If need be, the graduating may be done by simply pasting on the glass strips of paper, upon which a graduated scale has been drawn. The zero of the pipette's graduation is exactly at the lower extremity, B. The graduation of the two gauge tubes extends in both directions from a zero situated near the center. The zeros of the two branches must correspond as exactly as possible, so that they shall be in the same horizontal plane when the apparatus is fixed upon a support. To render the apparatus complete, it only remains to adapt, at A, a rubber tube provided with a wire clamp, and terminating in a short glass tube for sucking through with the mouth. [Illustration: PIPETTE FOR TAKING THE DENSITY OF LIQUIDS.]