Apparatus for calculating Efficiency . 193 



dye-stuffs, one of the hydroxyl groups must be in the ortho- 

 position as regards the ( — CO — ) group in order that the 

 compound may be a dye-stuff. For there are numerous iso- 

 mers of alizarin, but most of them are colourless, only qui- 

 nizarin and xanthopurpurin possessing tinctorial properties; 

 and in these, as well as in alizarin, one of the HO groups is 

 in the ortho-position, thus : — 



II I I 



00 CO CO CO 



J I 



OH 0H <^ 



OH OH 



Alizarin. Quinizarin. Xanthopurpurin. 



m.p. = 160. m.p. = 200. m.p. = 184. 



In the above sketch I have endeavoured to give a brief 

 account of the more important facts which have come to light 

 during late years in reference to the influence of chemical 

 constitution on the physical properties of organic compounds. 



I had intended saying something of this influence of atomic 

 arrangement on the specific volume of compounds and also on 

 the chemical activity, or the susceptibility of certain elements 

 or groups of elements in a compound being replaced by other 

 elements or groups of elements ; but my remarks have already 

 attained more than sufficient length, and to do these latter 

 subjects full justice would require the space of another paper. 



XXII. Apparatus for calculating Efficiency. By C. Vernon 

 Boys, A.R.S.M., Demonstrator of Physics at the Normal 

 School of Science, South Kensington*. 

 [Plate V.]. 



IN a previous paper I have shown how work done in an 

 engine or transmitted by shafting or belting, or ex- 

 pended by an electric current, or how the quantity of elec- 

 tricity which has passed in a conductor during any time, may 

 be automatically measured and integrated or recorded. The 

 present paper refers to apparatus for dividing rates of growth 



* Communicated by the Physical Society, hayiug been read at the 

 Meeting on January 28, 1882. 



