446 Notices of the Labours of Continental Chemists. 



Now the squares of the three semiaxes of the surface are the 

 three roots of this cubic equation, and as the last term is the 

 product of the roots with the sign changed, we find, calling 

 the semiaxes r 1 r" r 1 ", 



r 1 r" r 1 " = a b c, 



hence the volume of the ellipsoid = — - r' r" r" 1 = — a b c. 



r 3 3 



It is not difficult to show, that the areas of the sections of the 

 surface made by the coordinate planes are it a b, irac, and 

 it be respectively, and in general that the area of any conic 

 section whose equation is 



A 2 .r 2 + BV + 2ABcosv.#y = 1, 

 is independent of v, the angle between the axes of coordinates, 

 where A and B are the reciprocals of the segments into which 

 the line moving between the axes of coordinates is divided. 



From this known property that if a line of constant length 

 revolves between two fixed rectangular axes, the locus of the 

 middle point is a circle, may be deduced a method of con- 

 verting rectilinear into circular motion, rigorously exact, and 

 simple in construction, admitting an unlimited length of 

 stroke, and obviating the necessity of using a working beam 

 or connecting rod ; a change which would introduce a de- 

 cided improvement in the construction of the steam-engine*. 



LXXIX. Notices of the Results of the Labours of Continental 

 Chemists. By Messrs. W. Francis and H. Croft. 

 [Continued from p. 287.] 

 On Hematoxylin. 

 /^HEVREUL examined Campechy wood (wood ofHatma- 

 ^- / toxylin campechianum, L.) thirty years ago, and found in 

 it a crystallizable colouring principle which he called Haematin, 

 which name has been changed into Haematoxylin to avoid 

 any confusion with the heematin of the blood. Chevreul pro- 

 bably did not procure the body in a state of purity. Erdmann 

 has now examined it, and he proposes the following method 

 for its preparation: — The common extract of logwood is pul- 

 verized and mixed with a considerable quantity of pure sili- 

 ceous sand (to prevent the agglutination of the particles of the 

 extract), and the whole allowed to stand several days with five 

 or six times its volume of aether, the mixture being often 

 shaken ; the clear solution is poured off and distilled until 

 there is only a small syrupy residue. This is mixed with a 



* [The reader is requested to cotrect some oversights and errors in the 

 preceding part of this paper, it having been printed from an unrevised proof. 

 — Edit.] 



