Effects of Heal mod'ifinJ ly Ctmipression. QQ3 



((jxclude the fusible metal. But tlic rest of the carbonate, 

 contained in the large lube, came out in a fine state, being 

 porous and frothy throughout; bparkhng every where with 

 tacettes, the angular form of whi^-h was distinguishable m 

 some of the cavities by help of a Ipns : in some parts the 

 substance exhibited the rounding of hision ; in many it was 

 ill a higli degree transparent. It was yellow towards the 

 lower end, and at the other almost colourless. At the upper 

 end the carbonate seemed to have united with the tube, and 

 at the places oi" contact to have spread upon it, the union 

 having the appearance of a mutual action. The general 

 mass of carbonate efiervcsced iij acid violently, but the thin 

 stratum immediately contiguous to the lube, feebly, it at all. 

 On the 3d of March I introduced into a very clean tube 

 of porcelain 36-8 of chalk. The tube was placed in the 

 upper part of the cradle, the remaining space being filled 

 with two pieces of chalk, cut for the purpose; the upper- 

 most of these being excavated, so as to answer the purpose 

 of an air-tube. The pieces thus added were computed to 

 weigh about 300 grains. There was no pyrometer used, but 

 the heat was guessed to he about 30'^. After the barrel had 

 stood during a few minutes in its delivering position, the 

 whole lejid, with the rod and cradle, were thrown out with 

 a smart report, and with considerable force. The lowermost 

 piece of chalk had scarcely been acted upon by heat. The 

 upper part of the other piece was in a stale of marble, with 

 some remarkable facettes, The carbonate jn the little tube 

 had shrunk very much during the first action of heat, and 

 had begun to sink upon itself by a further advancement to^ 

 wards liquefaction. The mass was divided into several cy- 

 linders, lying confusedly upon caph other; this division 

 a.risiug from the manner in which the pounded chalk was 

 rammed into the tube in successive portions. In several 

 places, particularly at the top, the carbonate was very 

 porous, and full of decided air-holes, which could not have 

 been formed but in a soft substance; the globular form and 

 shining surface of all these cavities clearly indicating fusion. 

 The substance was semi-transparent ; in some places yeU 

 Ipw, and in sonie colourless. When broken, the#olid parts 

 T 4 showed 



