PRUSSIAN BLUE. PERPETUAL MOTION. 107 



tiful, than those from indigo. This chemist, after repeating the 

 fruitless attempts of his predecessors, is convinced, that from in- 

 digo alone, it is impossihle to obtain the various shades of pure 

 blue, the materials employed with the indigo changing the color, 

 so as to incline it, more or less, to a purplish or greenish hue. 



The following is the method pursued by M. Chevreul, in gradu- 

 ating the shades from Prussian blue : He impregnates each of the 

 different parcels of silk to be dyed, with ditferent proportions of 

 the oxide of iron, by immersing them in solutions, the strength of 

 which has been previously regulated. For the deeper tones of 

 color, he employs the acetate, and for the others, the muriate or 

 sulphate ; after having properly rinsed each of the parcels, they 

 are dipped into distinct vessels, or baths of the prussiate of potash, 

 the proportion of which has been made to correspond with the 

 quantity of oxide of iron previously united to each portion of silk. 

 By these precautions he obtains all the desired shades ; those, how- 

 ever, which are light, are apt to have a greenish hue ; but M. 

 Chevruel found, that on washing them sufhciently in river water, 

 the blue shade was obtained in perfect purity. When the washing 

 did not completely produce this effect, a very weak solution of 

 muriatic acid was found to remove the yellow matter which de- 

 teriorated the blue, and produced the tinge of green." 



yim. Mech. Mag. 



PERPETUAL MOTION— DISCOVERED ONCE MORE. 



Dr. Giraud, of Baltimore, announces that he has invented a 

 Perpetual Motion Machine. The following is his description of it : 



To Scientijic Mechanics, and olhrrs. 



The dead point is gained, and perpetual motion is discovered 

 by J. J. Giraud, Physician, of the city of Baltimore. It cannot be 

 denied. The thing itself is simple, and a tritiiiig expense will con- 

 vince the most incredulous. 



Description of the Perpetual Machine. — A sunk spur-wheel of a 

 certain diameter, with a round hole at its huh, is placed upon a 

 short round tube, which acts as a journal and shaft, and does not 

 pass the hub of the wheel. One end o{ this tube must be fixed 

 solidly on a plummer-block, and the other part supports the sunk 

 Spur-wheel. A shaft of a certain length, passes through this tube 

 by one of its sides, which is round ; and the part which fills ti)e 

 space of the tube, of tiie thickness of the hub, must be smaller, for 

 the purpose of leaving a certain space between the said shaft and 

 the inside of the tube, so that they may not touch each other. 



That part of the shaft which is outside and near the opening of 

 the hub and the wheel is square, and receives a large pinion of a 

 certain diameter. Between the large pinion and the sunk spur- 

 wheel, there is a very small pinion which works with the two 

 wheels. It is placed upon a long axle-tree, which is siij)ported by 



