r.V OHRISTOPHEB John- rOK. 13 



notice such guanos as contain sulphate of lime in any quantity, 

 but especially in large proportion. Algoa Bay Guano South 

 Africa), for instance, as furnished us by a reliable person, 

 found to consist almost wholly of this refractory substance, 

 which required an especial treatment. Being soluble in boiling 

 and hot dilute chlorhydric acid, it was found necessary to boil 

 the AJgoa guano in that dilution, aid to pour the whole on a 

 filter, whereby the sulphate of lime in solution ran off and 

 deposited on cooling, while the, guano residuum was caught by 

 the filter, to be subjected again and again to the same pi 

 as long as it contained the salt of lime. The small portion of 

 decalcified guano was next exposed to the action of NO 6 and 

 HC1, in the usual way, with the result of securing some beauti- 

 ful AcHnoptychi and Aidacodiscus Petersii. 



Pure gatherings, unmixed with sand, mud, or other refractory 

 extraneous substances, are not made t<» pass through the ordeal 

 of an alkali, and so many acids, as in the case of a guano, but 

 may be cleaned by the use of one of these agents with the aid 

 of no long-continued heat. Chlorophyll will yield to carbonate 

 of soda, and all possible lime here, to nitric acid; but when we 

 have to deal with wry delicate Amphipleuras or Grammato- 

 phoraSj marked with almost ghostly lines, we should handle 

 our reagents with gloves, and not boil out those exquisite 

 markings which almost rival the art-ruled bands of Nobert, 

 Maceration for a time may be sutlicient; or, if the quantity be 

 small, all phytic substance may be burned away by the heat of 

 a spirit-lamp flame applied beneath a film of mica, on which 

 the "once animated dust M reposes, and on which it may, with- 

 out change, be mounted in balsam. 



It is needless to remind the young operator of the necessity 

 for delicacy in all manipulative procedures, and not least in the 

 washings of pure gatherings, or of those containing the filmy 

 forms. But care is especially to be exercised in the 1- 

 those most fragile Diatoms which are met with in Barl 

 >',irih. Water al<>n<', poured gently on this polycystinoufi 



poeit, will suffice t«> float away and waft them to slides ready for 

 their reception. And this may be done in a beaker, ><» that the 

 Bupernatanl water, rendered milky by diatoms and siliceous 

 dust, yields by elutriation the fairest ^i results. 



