46 Mr Henwood on the Expansive Action of Steam 



engine at Huel Towan ; on Swan's engine at Binner Downs 

 mine ; and on Hudson's engine at East Crinnis mine.* These 

 were among the best engines in Cornwall, and they were se- 

 lected on account of the very varied circumstances under 

 which they worked. 



At Huel Towan, the cylinder with its cover and bottom 

 were surrounded with a case or jacket, filled with dense steam 

 from the boiler ; and these, with the steam-pipes, nozzles, &c., 

 were covered with saw-dust from sixteen to twenty inches 

 deep. The boilers had a layer of ashes, of about the same 

 thickness, placed on them. 



There was no steam-case at Binner Downs, but there were 

 small fires on each side of the cylinder, and the flues from 

 them were carried spirally round it ; another little fire was 

 placed beneath the steam-nozzle, from the boiler, and its flue 

 was passed over the cyUnder-cover ; under the steam-pipe 

 from the boiler was a similar fire, and its smoke was conveyed 

 round the pipe for some distance. Such parts of the engine 

 as were not enveloped by the flues were surrounded with saw- 

 dust,t and the boilers were covered with ashes as at Huel 

 Towan. 



The engine at East Crinnis had neither steam nor heated 

 air passed round it ; but every part which contained dense 

 steam was surrounded with a very thick covering of saw-dust, 

 and the boilers were protected in a similar manner to those 

 of the other engines. 



On all these the indicator was placed ; and also on Burn's 

 engine at Binner Downs, which is enclosed in a similar man- 

 ner to Swan's engine on the same mine, already mentioned ; 

 and on Trelawny's and Borlase's engines at Huel Vor, both 

 which have steam-cases and other coverings like that de- 

 scribed at Huel Towan. On the duty of these no experiments 

 were made. 



* The engineers were respectively, Mr Grose, Messrs Gregor and Tho- 

 mas, and Mr Sims. 



t In the progress of my experiment, the saw-dust on the cylinder-cover 

 ignited several times. The influence exercised on the steam within the 

 cylinders, by the media with which they were surrounded, may be disco- 

 vered by an inspection of the diagrams. (Figs. 4, &c. PI. IV.) 



