NEW INSTRUMENTS

A new microphotometer–spectroprojector has been designed at the Elektropribor plant in Leningrad by engineers G. P. Illarionov and N. V. Gablin. In this microphotometer the selenium photocell has been replaced by a Kubetsky tube, thanks to which photometry of low intensities is now possible in a darkroom. The instrument can serve not only for photometry, but also for projecting an enlarged image of a spectrum.

A new model of monochromator for the ultraviolet up to 2000 Å has been developed at the SOI by G. P. Ponomarev. The instrument is essentially constructed on the model of the Bausch and Lomb quartz monochromator. A significant innovation is the replacement of quartz prisms by silvin prisms. These prisms are protected from atmospheric moisture by quartz plates 1 mm thick, placed in optical contact with them. This choice of prisms considerably reduces the cost of the instrument.

The monochromator is equipped with achromatic quartz-silvin objectives (whose chromaticism, however, has not been completely eliminated). The slit construction is symmetrical.

A camera is supplied with the instrument, thanks to which it can also be used as a spectrograph. The linear dispersion is from 3345 Å to 2138 Å—43 mm at an aperture ratio of 1:4.5.

A new type of insensitive needle valve has been developed by F. Stolman and P. Kruger (University of Illinois) for maintaining the required pressure in a cyclotron.

The vacuum seal is a cone coated with grease. The needle rotates with the aid of an ordinary pin connection, fitted to several thousandths of an inch. The needle itself is a downward-tapering steel spindle 2 1/2 inches long and 1/4 inch thick, fitted to the opening. At the base of the opening there is a widening 1/8 inch in diameter and 1/4 inch deep. This widening is filled with an aluminum solder, and then drilled to 1/4 inch. The needle must be well ground and inserted tightly enough to be held in the solder. Such a valve requires 30 full turns from the closed position to obtain the required pressure in the cyclotron, whereas ordinary valves give this pressure with an opening of 1/4 turn.

A new cuvette for measuring absorption in the infrared region has been constructed by G. Randall of the physics laboratory of the University of Michigan for working with organic liquids. Instead of the cement gaskets usually used to create impermeability, Randall uses mercury. The demountable cuvette consists of two NaCl or KBr plates, between which an aluminum or platinum gasket is placed to determine the thickness of the liquid layer. In both plates, deep annular grooves are cut; when the cuvette is assembled these are superposed on one another and form a channel filled with mercury through an opening in the upper plate. When assembled, the cuvette plates are pressed against each other by screws (rubber gaskets are inserted for uniform pressure). The mercury seal proves sufficiently reliable to retain the liquid even when a vacuum spectrograph is used. The cuvette also has the advantage of being easy to clean.

A. Komarova, Moscow