202 THE ANALYST. APPARATUS. A New Gasometric and Absorption Burette for Technical Gas Analysis. 0. Tollens. (Chem. b i t . , xxviii., 303).-The chief novelty in the construction of the burette described is that its upper end is closed by means of a movable piston constructedof metal and rubber, which is made to fit tightly by means of a little oil. To make it firmer, the rod of the pieton passes through a cork placed in the upper extremity of the burette. The latter is graduated in such a way that it holds 100 C.C. from the zero division to the mark ( a ) placed a little above the stop-cock; it also holds 100 C.C. from the mark ( b ) in the upper part to the stop-cock. The burette is filled with gas to be examined through the side-tube (c), the piston being first drawn up above the latter.The piston is then brought down to ( b ) , and the gas pressure is equalized by opening the stop-cock for a moment, when the burette will hold exactly 100 C.C. of the gas. The absorb- ing reagents are sucked into the burette by raising the piston and opening the stop-cock; after absorption is complete, the burette is rinsed out with water, and the level of the water brought to (a), after which the volume is read off. To render readings easier to take, a, disc with sharp edges is placed at the lower end of the piston. The burette can be obtained from the firm of Gebr. Ruhstrat in Gbttingen. A. G. L.THE ANALYST. 203 The Nephelometer, an Instrument for Detecting and Estimating Opalescent Precipitates. Theodore William Richards and Roger Clark Wells. (Amer.Chem. Journ., xxxi., 235).-The apparatus described is designed to determine the quantity of precipitates when less than 1 or 2 milligrammes are suspended in 1 litre of solution. The method depends on the facts that these Precipitates reflect light, and that the intensityof the light reflected is a function of the quantity of precipitate, other conditions being constant. The apparatus consists of the main frame A , which holds in position the two tubes con- taining the liquids to be compared, a movable top B, containing two prisms, and a, large box C, in which is the source of light. The tubes themselves are clear glass test-tubes, holding 32 c.c., and painted outside around the top and bottom with black asphalt paint in order to oblite- rate reflections from the meniscus and the bottom of the test-tube.The space between the two bands should be the same in each case. The tubes can be completely covered by the sliding jackets S, S, made of glass thickly painted, and held in any desired position by a brass spring. On the two wooden pillars which support the test- tubes scales are marked, which indicate the length of each tube exposed to the I Tmnt light when the jackets are raised. The top B is light-tight, but easily removable. I t contains a small frame, which can be adjusted to any position by the screw R. This frame holds two 15' prisms, with their thin edges ground together. By looking down through the prisms half of each tube may be seen side by side. The length of tube exposed, or the strength of the standard solution used, is adjusted until the two halves appear equally bright. An incandescent electric light is used as the source of illumination. For stirring the liquids in the test-tubes, propeller-shaped pieces of platinum foil sealed upon glass rods are used. I n determining precipitates with this apparatus, they must always be precipitated under the same conditions, preferably in the test-tubes themselves, as otherwise the time elapsed since the precipitation may influence the reading. Results obtained with known amounts of silver chloride in suspension show the method to be exceed- ingly accurate. A. G. L.: