128 SCIENCE 1ST SHORT CHAPTERS. 



for no return of the mercury took place when the tube was 

 cooled. The depression was permanent. The formation of 

 vaporous carbon was suggested by one of the capitalists ; but 

 neither Mr. Starr nor myself was satisfied with this, nor with 

 any other surmise we were able to make during Mr. Starr's life- 

 time, nor up to the period of final abandonment of the enterprise. 



When this occurred the remaining apparatus was assigned to 

 me, and I retained possession of the finally arranged tube and 

 carbon for many years, and have shown it in action worked by a 

 small Grove's battery in the Town Hall of Birmingham, and many 

 times to my pupils at the Birmingham and Midland Institute. 



These exhibitions suggested an explanation of the mysterious 

 gaseous matter, which I believe to be the correct one, and also 

 of the carbon deposit. It is this : That the carbon contains 

 occluded oxygen ; that when the carbon is heated some of this 

 oxygen combines with the carbon, forming carbonic oxide and 

 carbonic acid, and a little smoke. I proved the presence of 

 carbonic acid by the usual tests, but did not quantitatively 

 determine its proportion of the total atmosphere. 



If I were fitting up another tube on this principle I should 

 wash it with a, strong solution of caustic potash before filling 

 with mercury, and allow some of the potash solution to float 

 on the mercury surface, by filling the tube while the glass 

 remained moistened with the solution. My object would be 

 to get rid of the carbonic acid as soon as formed, as the observa- 

 tions I have made lead me to believe that when the carbon 

 stick is incandescent in an atmosphere of carbonic acid or car- 

 bonic oxide a certain degree of dissociation and recombination 

 is continually occurring, which weakens and would ultimately 

 break up the carbon stick, and increases the sooty deposit. 



The large battery was arranged for intensity, but even then 

 it was found that the quantity (I use the old-fashioned terms) 

 of electricity was excessive, and that it worked more advanta- 

 geously when the cells were but partially filled with acid and 

 sulphate. A larger stick of carbon might have been used with 

 the whole surface in full action. 



After working the battery in various ways, and duly consid- 

 ering the merits of the other forms of battery then in use, Mr. 

 Starr was driven to the conclusion that for the purposes of 

 practical illumination the voltaic battery is a hopeless source of 

 power, and that magneto-electric machinery driven by steam- 

 power must be used. I fully concurred with him in this con- 

 clusion, so did Mr. King, Mr. Dorr, and all concerned. 



