Progress of Invention. 237 



step, until at length, he found the method of fixing, on any sub- 

 stance, by means of materials which become hygrometric under the 

 influence of light, carbon, metalHc oxides, and other impalpable 

 powders. And the development of this principle led to his disco- 

 very that a mixture of tartaric acid and perchloride of iron, which, 

 when acted on by light, becomes hydroscopic, is well suited for 

 fixing metallic oxides on enamelled plates, so as to give the ut- 

 most permanency to photographs, by transforming them into ena- 

 mels. Thus an immense stride in progress was made at once ; 

 perishable compounds of silver and gold being replaced by sub- 

 stances of the greatest durability. 



A Simplified Pump. — We have already * directed the attention 

 of our readers to one simplification of the com m on pump ; another, 

 which would seem to be still more generally applicable, is coming 

 into use. In the modification already alluded to, the valve in the 

 piston was rendered unnecessaiy ; in that we are about to notice, 

 the piston itself is discarded, The vacuum is obtained by means of 

 a diaphragm, which divides the suitably formed chamber of the 

 pump into two compartments. When the diaphragm is moved to- 

 wards one extremity of the chamber by a rod, one end of which 

 is attached to its centre, the space at the other side is enlarged, a 

 vacuum being formed, and water rushes in through a valve to fill 

 up this vacuum. When the diaphragm is moved by the rod in the 

 opposite direction, the water which has just entered is driven for- 

 ward in any required direction ; a vacuum being at the same time 

 formed at the other side of the diaphragm. The movement of the 

 rod, therefore, in each direction causes both water to enter the 

 chamber to fill up the vacuum, and water to be forced from the 

 opposite side of the chamber. The action is, by consequence, both 

 as to suction and forcing, almost continuous. 



Production of a Vacuum bt Means of Ammonia. — The empty- 

 ing of the cesspools in Paris has always been attended with great 

 inconvenience. Among the methods proposed for obviating this, 

 has been the use of air-tight tanks as carts, the causing a vacuum 

 within them by pumping out the atmospheric air, and then filling 

 them, when arrived at the cesspool, by atmospheric pressure. In 

 theory this method was excellent, in practice it was found impossi- 

 ble to maintain the vacuum for the required length of time. M. 

 Tellier, who suggested liquified ammonia as a source of motive 

 power, f considers that gaseous ammonia may be used for the produc- 

 tion of a vacuum in these tanks. For this purpose, he would have at 

 the establishment whence the carts are to be despatched, a boiler con- 

 taining water of ammonia. From this, gaseous ammonia is to be 

 liberated by heat, and transmitted to the tank in which it is in- 

 tended to form the vacuum. The atmospheric air is thus driven 

 from the interior of the tank ; and any ammonia that may pass off 

 along with it is to be retained by water, through which the mixture 

 is passed for the purpose. Ammonia is allowed to enter the tank, 



* Intellectual Obseevee, No. xxxvii. p. 78. 

 f Intellectual Obseevee, No. xxxviii. p. 14S. 



