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HARD WICKE 'S S CI EN CE-GO SSI P. 



of distilled water ; and in order to avoid this, the 

 water should be poured into a clean test-tube, or, 

 preferably, into an ordinary graduated glass measure. 

 I would also remark that it is more economical to 

 use small quantities of water at different times than 

 a larger quantity at once, although, of course, it takes 

 somewhat longer to get rid of the acid.) When the 

 water no longer shows any trace of acid, pour off 

 and replace it with liquor ammonice,* cork up the 

 test-tube and allow the diatoms to remain in it for 

 from half an hour to nine or ten hours : the time 

 will, of course, depend on the delicacy of the forms. 

 Although ammonia is not so injurious as soda or 

 potash, it will in time destroy the diatoms ; it is," 

 therefore, better to pour off a little too soon than too 

 late. When the ammonia is decanted, fill the tube 

 with water and shake well, and if it is desirable to 

 separate the clean diatoms into densities, it should 

 now be done. Pour into another tube all that have 

 not reached the bottom of the tube in five minutes, 

 - (If the gathering contains very large and stout forms, 

 from one to two minutes will be long enough.) Ten 

 minutes may be allowed for the next density, and 

 should there be any veiy minute diatoms, at least an 

 hour should be allowed for their subsidence. The 

 water last poured off will contain the connecting 

 zones and flocculent matter (the latter is sometimes 

 held in suspension for several days). We have now 

 three or four test-tubes, each containing diatoms of 

 different sizes, and also ammonia : this must be 

 got rid of before mounting. If the material is valu- 

 able, it is best to begin with the heaviest density. 

 Fill the tube about one-third full, shake it, allow the 

 same time as before for subsidence, then decant into 

 the next density ; continuing the process with the other 

 densities. 



Unfortunately, diatomaceous gatherings generally 

 contain the debris of various algae, mosses, leaves, 

 microzoa, &c. In collections made from fresh-water 

 sources the process just described is usually suf- 

 ficient to eliminate the extraneous substances, parti- 

 cularly if the gathering is strained through a piece of 

 muslin, previously macerating it in hydrochloric acid 

 and water ; but those from marine habitats, such as 

 dredgings, stomachs of ascidians, salpce, noctilucae, 

 or moUusca, require sulphuric acid for the entire 

 destruction of the organic matter. 



I have generally found the following process suc- 

 cessful. If the material contains much animal matter, 

 it is best to give it a preliminary boil in a solution of 

 bicarbonate of soda (half an ounce to two ounces of 

 water), and filtering through a piece of fine net : add 

 more water and allow the solid matter to subside ; 

 boil the residuum in nitric acid, wash away the acid, 

 and, after pouring off the water as closely as possible, 

 add sulphuric acid (this must be done with care : 



• A small quantity is usually sufficient : enough to cover the 

 diatom about half an inch will do. 



if added too rapidly, steam will be suddenly generated 

 and a portion of the contents of the tube scattered 

 about), and boil until the organic matter is carbonized. 

 If this exists in any quantity, the material will become 

 black ; small pieces of chlorate of potash must now 

 be dropped into the tube, allowing the effervescence 

 to subside before using a second piece. This must be 

 continued until the contents become white, or decar- 

 bonized. The whole should now be slowly poured 

 into warm distilled water and washed as previously 

 described. If the residuum, when free from acid, 

 should contain any crystals of sulphate of potash, a 

 further boil in nitric acid will dissolve them. 



In guanos Ehrenberg discovered many rare and 

 beautiful forms of diatomacea;, which he described in 

 a communication to the Berlin Academy in 1844. 

 Unfortunately, in guanos, the amount of organic 

 matter is very large, and ofTers considerable diffi- 

 culty to the tyro ; and most pf the recent samples 

 it is almost impossible to make sufficiently clean to 

 allow of mounting anything but picked specimens. 

 One of the earliest discovered guanos was that on 

 the island of Ichaboe, on the west coast of Africa 

 (26° 19' S. lat., 14° 15' E. long.) ; and if any of the 

 original samples are still in existence, they would 

 well repay the trouble of cleaning. This guano 

 speedily became of little value to the diatomist, and 

 is, I believe, now entirely worked out.* The guano 

 from the Chincha Islands and Arica, commercially 

 known as Peruvian guano, f was also veiy good, and 

 not very difficult to clean. I adopt the following plan 

 for that purpose (I usually operate on about two oz.). 

 I wash away all the soluble matter by boiling in hot 

 water (a Florence flask is very convenient for this 

 purpose). A small piece of carbonate of soda in 

 each boiling will be found advantageous. The in- 

 soluble residuum may now be treated with nitric acid : 

 this must be added in small quantities, as consider- 

 able effervescence ensues, and, if poured on too 

 quickly, considerable waste of acid and material 

 will occur. The sulphuric acid process must be used 

 after the nitric acid has been got rid of : when there 

 is much lime in the guano, as, for example, that from 

 Algoa Bay, a boil in hydrochloric, before using nitric 

 acid, is desirable. 



The fossil deposits may be divided into two kinds ^ 

 those which are of comparatively recent date, to 

 which class belong the subpeat deposits, of which so 

 many kinds are found in America, and the marine 

 deposits, such as those occurring in Virginia, Cali- 

 fornia, Oregon, Barbadoes, and many other localities. 

 Most of these require what the late Professor Bailey 

 called "heroic treatment." A preliminary boil in 

 nitric acid, to eliminate the lime, is generally neces- 

 sary. Sometimes this is sufficient to break up the 



* Genuine samples of this guano were found to contain from 

 I'oS to 2 per cent, of siliceous matter (sand and diatoms), 

 t Peruvian guano contained from i to i '46 of siliceous matter, 

 ! principally diatoms 



