282 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE. 



1. Method for Cleaning Diatomacece ; b} r E. R. Darling 

 (communicated). — There are a number of methods to be found in 

 various books on microscopy for cleaning diatomaceaB. None of 

 which proves to be perfect in all details. The method generally 

 resorted to is to boil with nitric acid. This does not, however, 

 remove all of the organic matter, and leaves a mounted specimen 

 contaminated with black specks. Another method is to boil the 

 specimen with sulphuric acid and potassium chlorate. This too 

 has its disadvantage as in boiling neutral potassium sulphate is 

 formed, this salt being sparingly soluble in water. The follow- 

 ing method, which is a modification of that of Edwards,* will be 

 found to work with great success. 



The sample is first dried, and then about five grams taken and 

 well washed with distilled water. The washing is best done by 

 placing the sample in a filtering paper fitted to a glass funnel, and 

 replacing the water as it runs out. The washing is complete 

 when about 250 cc has run through. A hole is then punched in 

 the apex of the filter paper and the sample washed into a 250 cc 

 beaker with concentrated hydrochloric acid, about 50 cc being 

 required. This is allowed to boil gently for 30 minutes, 100 cc of 

 hot water is then added, and the whole filtered. The sample is 

 washed with hot water until it gives no white coloration when a 

 drop is added to a weak solution of silver nitrate. The sample 

 left on the filter paper is then washed into the beaker with 50 ec of 

 concentrated nitric acid and gently boiled until red fumes cease to 

 be given off. This is then diluted with hot water, filtered, and 

 washed until free from acid. 



The above method removes all the mineral matter except silica 

 diatomacese, and a large part of the organic matter. The product 

 from the last operation is removed to a beaker by means of a 

 small spatula. To this is added a mixture of concentrated sul- 

 phuric acid and water, 8 parts of acid and 2 parts of water. In 

 mixing care should be taken to add the acid to the water. This 

 is boiled for about 30 minutes, or until the organic matter is 

 charred. As soon as the acid starts to boil weigh out about 2 

 grams of potassium chlorate and add to the acid in small quanti- 

 ties until the solution becomes colorless. The acid solution is 

 then poured into 250 cc of distilled water, filtered, and washed 

 free from acid. The product is then washed into a beaker with 

 about 20 cc 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, w T hich 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 

 sulphate 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 diato- 

 macese should be kept in a mixture of 6 parts of alcohol and 4 

 ]>art< of water to prevent them from matting together. 



* Quart. Jour. Micr. Sci., vol. vii. 



