Planetary Wheel. —'Mercuridl Solutions. 405 



On the largest of thefe two cones let the circles generated hj the revolution of the 

 points P, T, Q» be marked and diftinguifhed by the fame numerical figures as the cor- 

 refponding parallels of the parallelogram L O. 



Defcribe upon the two bafes of the conical fruftum radial lines, which fhall make angles 

 at the centre C, Fig. 3, in the fame proportion to each other as the intended velocities of 

 the wheel, as exprefled in Fig. 2> and let teeth be cut in the furface of the cone according 

 Vith thefe lines ; after which look on the circles which exprefs the diiFerent velocities, 

 and have been traced on the fame furface, to find what part of each tooth ought to 

 remain oppofite its correfponding radius, and cut or file away the reft. The teeth will 

 thus lie in an elliptical or inclined curve on the conical face, which in the figure is marked 

 by, a darker {hade. 



The pinion muft be made of a regular conical form, as is fliewn at M O, in Fig. 3. 



By this contrivance the largeft or wideft teeth will always meet the largeft part of the 

 pinion, and the narroweft will corrcfpond with the fmalleft part ; by which means, 

 though the pinion has an uniform motion, the wheel will be carried unequably, according 

 to the required law *. 



V. 



On the Solutions and Precipitates of Mercury. By Cit. Berthollet\. 



W, 



HITE fulphate of mercury, flightly oxided, as defcribed by Citizen Fourcroy in the 

 laft volume of the Academy of Sciences, is obtained with more eafe, and in a purer ftate, 

 by boiling very diluted fulphuric acid upon mercury. When the liquid undergoes a ftrong 

 heat, it becomes oxigenated fulphate of mercury. When there is not too great an excefs 

 of acid, it is in part decompofed by the water, which beomes acid by feizing a portion ' 

 of the acid. It, however, contains lefs acid than the mild fulphate. The proportions 

 between the precipitated oxided fulphate, and the acid fulphate fufpended in the water, 

 are different, according to the temperatures, the quantity of water, &c. 



When the fulphate is decompofed by an alkali, the precipitated oxide always retains 

 a fmall quantity of acid. 



Nitric acid has the fame habitudes with the oxides of mercury. Citizen Gay has 

 remarked, that when mercury is diffolved by heat in nitric acid, there is firft a difengage- 



* The contrivance of DefaguKers, defci ibed in liis Courfe of Experimental Philofofhy, I. 464, confifts of 

 two elliptical wheels. Fig. 4 and 5, connected by tooth or by catgut (which laft is a very bad way.) They 

 revolve on their foci, and while the driving eilipfis moves uniformly, the radius ve^or of the other has the 

 required motion. ---R. B. 



-(- Societe Philomath. No, j^^ 



ment 



