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108 



THE AMERICAN MONTHLY 



De and ■ 



or they are given in such an em- 

 pirical manner, that the beginner is 

 at a loss to know how to proceed in 

 ordinary cases; he can only fol- 

 low the directions, blindly adding 

 acid after acid because he does not 

 know the effect of the different 

 acids. 



In this article it is proposed to 

 not only give such directions as will 

 serve well for such diatomaceous 

 material as the collector is most 

 likely to meet with, but also to 

 briefly explain the action of the 

 chemicals employed, so that a per- 

 son of ordinary intelligence may 

 know how to vary the processes to 

 suit special cases. 



We will not now refer to the 

 methods of collecting diatoms, but 

 will proceed at once to describe the 

 process of cleaning them. 



We may have them in the form 

 of fresh gatherings, or as fossil de- 

 posits ; the method of cleaning 

 will be different in the two cases. 



The object of cleaning is : first, 

 to remove all extraneous matter 

 from the f rustules, so that they will 

 appear clear, and all their minute 

 markings will be seen to the best 

 advantage ; second, to remove par- 

 ticles of sand and dirt which would 

 mar the beauty of the slide. Un- 

 doubtedly the first is the more 

 important object of cleaning, but 

 many mounters are too fastidious to 

 be contented with that alone. How- 

 ever, it should be remembered that 

 not every gathering, whether recent 

 or fossil, can be freed from particles 

 of insoluble dirt or sand, and this is 

 often the case with collections which 

 contain rare forms. Consequently 

 a preparation should not be con- 

 demned because it is not entirely 

 diatomaceous. It may be valuable, 

 and some of the most remarkable 

 and interesting forms we have seen, 

 forms which we have studied by 

 the half-hour on account of the ex- 



quisite beauty of their shape and 

 markings, were isolated specimens, 

 on a slide containing much debris. 



Moreover, even when the mate- 

 rial can be cleaned very well, it may 

 be that the quantity in hand is so 

 small that the best results cannot be 

 attained. Many have tried to clean 

 the celebrated Richmond deposit 

 and have failed, partly because they 

 worked with too little material, and 

 partly, no doubt, because their speci- 

 men was not well selected, for not 

 all of that deposit will give very 

 clean slides. 



A diatom consists of a siliceous 

 f rustule, which for our purpose may 

 be considered as composed of pure 

 silica ; and the endochrome. As 

 to the endochrome, we may regard 

 it as organic matter containing a 

 trace of iron ; in cleaning the dia- 

 toms we have to destroy the organic 

 matter, and to remove the iron by 

 solution. 



NITRIC ACID PROCESS FOK FKESH 

 GATHERINGS. 



Only the simplest process of clean- 

 ing, therefore, is necessary, when 

 we have to work with fresh gather- 

 ings that are purely diatomaceous. 

 The iron of the endochrome is 

 in solution, and will give us no 

 trouble to remove, for any dilute 

 acid will take it out at once. Hence, 

 we need only remove the organic 

 matter. This is readily done by 

 boiling the moist or dried gathering 

 in strong nitric acid, and this is all 

 that is necessary to do, if we wish 

 to clean a pure gathering of dia- 

 toms that are mixed with a con- 

 siderable quantity of other vegeta- 

 ble or organic matter. Nitric acid 

 is an oxidizing agent, and it burns 

 up and destroys the organic matter 

 of the diatoms, while it also dis- 

 solves the small quantity of mineral 

 matter with which they may be 

 contaminated. In this process it 



