ZOOLOGY AND BOTANY MICROSCOPY, ETC. 501 



of concentrated hydrochloric acid, and gently boiled for about 15 minutes. 

 It is then diluted with hot water, filtered, washed first with distilled 

 water acidified with hydrochloric acid, and then with hot water until 

 free from acid, which is determined by adding a drop of a weak solution 

 of silver nitrate. 



By the addition of the potassium chlorate to the sulphuric acid 

 solution the organic matter is destroyed. The neutral potassium sul- 

 phate which is formed is changed into the chloride by the addition of 

 the hydrochloric acid. The chloride is soluble in hot water and is 

 removed in this way. When thus purified the Diatomacese should be 

 kept in a mixture of 6 parts of alcohol and 4 parts of water, to prevent 

 them from matting together. 



New Water-jet Air-pump, and the Fixing and Embedding 

 of Microscopical Objects in vacuo.*— M. Wolff describes a new 

 water-jet air-pump recently placed on the market by the firm of Erich 

 Koeller, of Jena. The working principle consists in the fact that the 

 entering jet of water passes with a whirlpool action round a glass funnel, 

 into which the tube connected with the evacuation vessel fits. This 

 tube is fitted with a reaction valve to prevent the overflowing of water 

 into the vacuum. The apparatus is very powerful. A 2-litre vessel 

 with 720 mm. air-pressure and '1'b to 3 atmospheres water-pressure 

 (and a water temperature of +13° C.) is evacuated up to 711 mm. 

 mercury in seventy seconds. This apparatus is especially useful for 

 fixing and embedding tissues in vacuo. Delicate structures (larvae of 

 arthropods and the like) are particularly suitable for vacuum embedding, 

 as the processes are very much shortened and a minimum amount of 

 injury is sustained by the tissues. 



(3) Cutting-, including' Embedding- and Microtomes 



Leitz's New Rotary Microtome.f — S. Becher describes this appa- 

 ratus in the course of an article on New Microtome Constructions. 

 In this instrument (Figs. 50, 51), the delivery of the object part is 

 combined with a circular cutting motion together with a push and drop 

 movement of the knife. This combination gives to the instrument its 

 individual character and distinguishes it from older types, and not only 

 guarantees extraordinary facility but also astonishing uniformity of 

 action. The object part consists essentially of a metal disk about 8 mm. 

 thick and of 14 cm. diameter, whose perpendicular axis is secured above 

 and below by a tapering steel bolt, thus securing easy rotation without 

 the least vibration. The under bolt is attached to the base-plate, but 

 the upper is inserted into a strong cast-iron arm whose other end is 

 likewise attached to the base-plate. This arm is bent in such a way 

 that the object clamped to the disk can easily pass under during the 

 rotations. The object-clamp is rotatory about its axis and is universally 

 inclinable ; it is attached to a brass block, shaped like a segment of a 

 sphere, which itself has a universal movement in a corresponding saddle 



* Zeitschr. wiss. Mikrosk., xxxi. (1914) pp. 19-22. 



t Zeitschr. wiss. Mikr., xxxi. (1914) pp. 103-13 (2 figs.). 



