SCIENCE-GOSSIP. 



173 



accomplished by either of the three following 

 methods : by exposure to hard frosts ; by means 

 of the crystallization of certain chemical salts ; or, 

 by the use of mineral acids, either hydrochloric or 

 nitric — but hot sulphuric. In many instances the 

 employment of hydrochloric acid will alone suffice 

 to bring them to the desired condition; indeed, as 

 an invariable rule this acid, should, first of all, 

 be applied to the substance to be operated upon, 

 whether recent or fossil. This is to remove every 

 trace of solid calcareous matter by its conversion 

 into the very soluble chlorate of lime. If dis- 

 integration is the result of its application, then 

 the operator's work is greatly lightened ; but if, 

 when all effervescence has ceased, the lumps 

 remain in about the same state, after well washing 

 to remove all traces of acid and lime, they may be 

 submitted to the action of frost. 



By this process the lumps must always be well 

 soaked in water, then, half immersed, exposed in 

 a saucer or other shallow vessel in some open spot 

 until hard frozen. So- soon as ,the contents of the 

 vessel are thus congealed the whole may be placed 

 in a warm situation, say, on a fireside hob or in a 

 hot oven. Upon the melting of the ice it will 

 immediately be seen that the lumps readily crumble 

 with a touch. One exposure will, however, seldom 

 suffice, and occasionally it is desirable to submit 

 the material to the freezing and thawing process 

 three or four times. It is evident that this plan is 

 not generally practicable ; other means must there- 

 fore be employed. This is usually done by the 

 use of certain salts, which by their crystallization 

 break down the hard lumps without injury to the 

 diatoms. The chemicals mostly used are either 

 common saltpetre, i.e. nitrate of potash, or Glau- 

 ber's salts, i.e. sulphate of soda — preferably the 

 last. These salts contain a large quantity of 

 water of crystallization ; the crystals are large and 

 quickly formed ; their action, therefore, upon the 

 lumps submitted to them is rapid. The material 

 must be dropped into a hot, nearly saturated 

 solution, and should there be allowed to remain 

 for some considerable time ; if for several hours so 

 much the better. The solution and lumps should 

 then be set aside in a cold spot, and be undisturbed 

 until thoroughly crystallized. Upon submitting to 

 heat to dissolve the crystals, as in the case of 

 frozen materials, it will be seen that the lumps 

 have been fissured in every direction. More often 

 than not, however, the process has to be repeated, 

 occasionally five, six, or more times, until the 

 disintegration is complete. This will depend upon 

 whether or not the solution has thoroughly pene- 

 trated into the very heart of the lumps. So 

 compact, by the enormous pressure to which they 

 have been subjected, are the materials of some 

 rocks that I have known lumps no larger than a 

 small walnut to remain perfectly dry in the centre 



after soaking in water for many weeks. This I 

 have proved by splitting open. Hence the frequent 

 failure to disintegrate by two or three exposures to 

 the crystallizing process. This once complete the 

 solid matter should be allowed to subside. The 

 fluid should be carefully decanted and a liberal 

 supply of clean rain or distilled water added. 

 After a good stir up and a few hours allowed for 

 deposit of sediment, the water must be again 

 poured off and this repeated so long as any taste 

 of the chemical used remains. 



Disintegration accomplished, the material — well 

 washed — is ready for boiling, and may be trans- 

 ferred to the Wedgwood vessel (or beaker, if 

 preferred, but I never use this latter vessel 

 for sulphuric acid treatment), and allowed to 

 settle. Then as much of the fluid as possible 

 should be poured off, and to the residue two or 

 three times as much sulphuric acid should be 

 added. Immediately a violent commotion takes 

 place, the heat generated converting a portion 

 of the moisture in the material into steam. This 

 action soon ceases, and the vessel may be at 

 once placed over the lamp or stove, but must be 

 carefully watched to see that the contents do 

 not boil over. By degrees the ebullition ceases, 

 the whole of the water has been expelled from the 

 mixture, and nothing remains but the material and 

 acid. When this point is reached the acid barely 

 bubbles, and the whole is converted into a thick 

 jet-black fluid, or semi-fluid, the result of the car- 

 bonization of the organic matter, dense suffocating 

 fumes of acid being evolved. At this point chlorate 

 of potash may be added, either in powder or in 

 solution. 



The action of the chemicals upon each other is 

 twofold ; the sulphuric acid, having a strong affinity 

 for the potash, at once seizes upon it, and chlorine 

 gas is liberated, this latter converting the jet-black 

 into a snow-white fluid. The process is neces- 

 sarily a slow one, for but a very small portion of 

 either the chlorate powder or solution must be 

 introduced at a time. If the powder be used de- 

 crepitation takes place, and the operator must be 

 careful to avoid accidents. To begin with, let him 

 try a pinch each time, introduced by a spcon or 

 piece of wood. When the solution is used, much 

 greater care must be exercised, as, apart from the 

 chemical action, the sudden introduction of a cold 

 solution into boiling sulphuric acid at more than 

 6oo° Fah. immediately converts the solution into 

 steam, explosions follow, and showers of scalding 

 particles of acid are scattered. Even when the 

 solution is added drop by drop portions of the 

 contents of the vessel are ejected, sometimes to 

 long distances. I usually hold before my face a 

 sheet of glass when operating with the solution, 

 but would recommend the young amateur to con- 

 fine himself to the use of the powder. When the 



