ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 497 



of chloroform at its boiling temperature about 58° C, which is exactly 

 right for the melting of the paraffin. Since the tube of the flask is 

 open to the air, the temperature within cannot rise above that of the 

 boiling point of the chloroform in air, which rises only slightly with the 

 barometer. Practically all the chloroform is condensed and flows back 

 into the flask. 



A piece of cardboard may be placed over the flask to keep the dust 

 out of the paraffin, and a towel is usually thrown over it to conserve the 

 heat when warming up the bath. It takes about half an hour in a room 

 at 16° C. to melt the paraffin. After it is once warmed up it maintains 

 an invariable temperature, except on very cold days (5° 0.) 



The advantages of this new form of bath are : — 1. Simplicity: the 

 bath requiring no adjustment, and having no mechanical apparatus to 

 get out of order. 2. Precision of regulation, since no variation of tem- 

 perature in the heating medium occurs such as is necessary in an 

 apparatus with a mechanical thermostat. 3. Illumination of cup : a 

 convenience in handling the object in filtrating and an aid in keeping 

 the cup clean. 4. Inexpensiveness, the cost of the whole equipment 

 being not over 10s. 5. Safety, the heat being by electric lamp and the 

 regulating fluid being non-inflammable. 



Improved Method of Cleaning Diatoms.*— Diatoms, says John M. 

 Blake, are microscopic organisms near the dividing line between 

 animals and plants. It is important for our purpose that they have 

 siliceous skeletons which take on very many symmetrical and beautiful 

 shapes. The chlorophyll and organic matter with which they are 

 associated can be destroyed by strong acids, but they still retain the clay 

 and sand which were deposited with them. The process of cleaning 

 consists in removing this foreign material. Unless this be done the 

 forms will be obscured and difficult to detect. 



Many observers have studied and classified the numerous species, 

 and have spent much labour in preparing and mounting them for observa- 

 tion, for there is a fascination in these forms that appeals to all, and 

 any plan for facilitating and lessening the labour of preparation would 

 be likely to induce many more to take up the study. 



An ordinary well-known method of separation is to digest the 

 material with an acid, and then to dilute with water, and allow the 

 heavier portions to deposit. After an interval, the lighter portions are 

 poured away, and the process repeated until the clay, very fine sand, and 

 broken diatoms have been removed, while those diatoms which have not 

 been floated away during the process, remain with the coarse sand. 

 This process takes up considerable time, and requires careful attention 

 and timing to decant successfully, and, in spite of this care, some of the 

 smallest and lightest forms can hardly fail to be lost. 



The method now to be described was originated by the writer some 

 twenty years ago, and recently, in recurring to the subject, it seemed 

 that even at this date the method might appear novel, since it has not 

 been exhibited during the interval, and no mention of a similar plan 



* Amer. Journ. Sci., xxxv. (1913) p _>. 19-22. 

 Oct. 21st, 19 U 2 L 



