26 DIATOMA( 1 :.i . 



cals; but at any rate care must be taken not to drop any of the 

 acids upon the clothes or skin, and great caution must be exer- 

 cised in not inhaling any of the vapors given off. Those 

 evolved after the addition of the hydrochloric acid are especially 

 irritating and dangerous, and must be avoided. As soon as the 

 liquid has cooled a little, water should be added cautiously, as 

 great heat will be generated thereby, and there will be danger 

 of its boiling over. Thereafter it may be poured into a large 

 beaker-glass of water and thoroughly washed, as in the former 

 case. If it be found that the precipitate is not quite white, it 

 will be necessary to boil it again in sulphuric acid, with bi- 

 chromate of potash and hydrochloric acid, until it is quite 

 clean. If, on examination by means of the microscope, it is 

 found that there is much rlocculent matter present besides the 

 diatoms and sand, this can be removed by boiling for a few 

 seconds in a weak solution of caustic potash, and washing 

 quickly and thoroughly with plenty of clean water. When we 

 have recent gatherings of filamentous or stipitate forms of 

 diatomacere, which we desire to preserve in the nataral con- 

 dition, they should be immersed for about twenty-four hours in 

 alcohol to dissolve out the endochrome. If this does not 

 answer, it will be well to soak the mass of diatoms or plants 

 upon which they are adherent in a solution of hypochlorite of 

 soda, an impure variety of which is sold in the shops under the 

 name of Labarraque's disinfectant, for about the same length 

 of time. This will generally destroy all color, and leave the 

 specimens transparent. It is best, however, in many cases not 

 to remove the endochrome, but leave it, and mount the speci- 

 mens in such a way as to show them in as natural a condition 

 as possible. How this may be done will be described here- 

 after. 



Guanos. The preparation of these substances so as to obtain 

 the microscopic organisms they may contain is rather difficult, 

 tedious, and dirty, and should only be undertaken by a person 

 somewhat versed in chemical manipulations, and in a proper 

 room as a laboratory, where there is no danger of harm result- 

 ing from the fumes evolved. As the ammoniacal guanos are 

 those which contain the most diatoms, and consequently which 

 answer best to clean, we will begin with them, and take as a 



