108 REPORT— 1844. 



quent upon the acts of cliarging, stirring and raking the fires. These are 

 exemplified by the annexed diagrams, No. XII. and No. XXX. (Plates 

 XXVIII. and XXIX.) 



On a careful examination of the diagrams, it will be found that the first 

 was traced without any admixture of air, except that taken through the 

 grate-bars ; the other was inscribed with an opening for the admission of air 

 through a diffusing plate behind the bridge, as recommended by Mr. C. W. 

 Williams. The latter, No. XXX., presents very different figures : the maxi- 

 mum and minimum points of temperature being much wider apart in the one 

 than the other, as also in the fluctuations which indicate a much higher tem- 

 perature, reaching as high as 1400°, and seldom descending lower than 1000°, 

 giving the mean of 1160°. 



Now, on comparing No. XXX. with No. XII., where no air is admitted, 

 it will be found that the whole of the tracings exhibit a descending tempe- 

 rature, seldom rising above 1100°, and often descending below 900°, the 

 mean of which is 975°. This depression indicates a defective state in the 

 process, and although a greater quantity of coal was consumed, (2000 lbs. 

 in 396 minutes in the No. XXX. experiment, and 1840 lbs. in 406 minutes 

 in No. XII.,) yet the disparity is too great when the difference of tempera- 

 ture and loss of heat are taken into consideration. As a further proof of the 

 imperfections of No. XII. diagram, it is only necessary to compare the quan- 

 tities of water evaporated in each, in order to ascertain the difference, where 

 in No. XII. experiment 50.5lbs. of water are evaporated to the pound of coal, 

 and in No. XXX. one-half more, or 7*7 lbs. is the result. 



Taking the results thus indicated, it will appear evident that the admis- 

 sion of a certain quantity of atmospheric air behind the bridge operates most 

 advantageously, inasmuch as it combines with its constituents in due propor- 

 tions, and by these means the gases are inflamed under circumstances favour- 

 able to the extraction of heat and consumption of smoke. The whole pro- 

 cess is therefore distinguishable by the fact of one diagram presenting a 

 decreasing temperature when air is not admitted, and the other an increasing 

 column when it is introduced. If no air is admitted, except through the 

 grate-bars, and there happens to be a compact charge in the furnace, the 

 consequence is that the gases pass through the flues unconsumed, and ac- 

 companied with a dark volume of smoke which is invariably present on such 

 occasions. 



It will not be necessar}^ in this instance further to increase the number of 

 diagrams, as No. XII., which exhibits the variations and results of the in- 

 tensity of heat when air is not admitted; and No. XXX. (with an aperture 

 of fort3'-five square inches constantly open) will be found encouraging 

 features for its admission in duly regulated proportions. These two diagrams 

 will therefore sufficiently explain the varied changes of temperature which 

 exist, and as all the other thirty are (with occasional deviations) nearly alike, 

 the following table of results will probably answer the same purpose as if 

 the whole were given in detail. 



