GOLD (CHLORIDE OF). • GroDt difficulty has hitherto occurred in preparing the chloride of gold, of the yellow and red colors, perfectly soluble in water, and without suffering reduction. The follow ing processes are recommended for this purpose:— 1st. In order to prepare the yellow salt of gold, take aqua regia with three parts of hydro-chlorie acid, one part of nitric acid, and one of distilled water. Then put one part of pure gold into a porcelain capsule with a plate of glass, and heat it in a salt water bath, the heat being continued till red vapors the cover is then to be removed, and if the gold is not entirely dissolved, some aqua regia is to be added to it, the cap sule being again covered, the heat is to be continued till vapor ceases to appear and the glass plate must then be removed and replaced by folds of blotting paper, the heat being continued in the bath, until a glass rod, upon being immersed in the capsule, becomes covered with yellow solid chloride of gold.
The capsule is then to be removed from the salt water bath and the chloride of gold soon crystallizes in small prismatic crystals, of a fine yellow color, with an orange tint. The chloride thus obtained is perfectly soluble in water without re duction; it is successfully employed in Daguerreotype and other operations.
The red chloride of gold (ter-chloride) is prepared in the same manner, except that the aqua regia employed is prepared with two parts of hydro-chlorie, and one part of nitric acid. The operation is commenced by acting upon gold with excess of aqua regia on a sand bath, the salt water bath not being used until the gold is entirely dissolved • the remainder of the operation hi conducted in the same manner as that for the yellow chloride. GOVERNOR. A contrivance for gulating the speed of machinery, which has long been in use in mill-work, but has of late years attracted more attention by its adaptation to the steam-engine. It consists of two heavy balls B B, attached to the ties of two rods B F, B F, which play upon ajoint at E, passing through a tise in the cal shaft D D. These are united by joints at F to the short rods F II, which again are ed by joints at H to a ring, which slides on the shaft D D. A horizontal wheel,
W, is attached to D D, having a groove to receive a rope or strap on its rim, by means of which the motion is commune sated to D D from a corresponding wheel on some shaft of the machinery to be gulated. It is evident, from the tion of the rods, that if the balls B B are by any means raised or drawn asunder, the extremities F F of the rods turning on the pivot E will also be separated, and their distance from the axes increased. This will draW the rods F H in the same direction, and cause the ring or collar II to descend. This ring is connected with the end I of a lever, whose fulcrum is at G, and whose other extremity K is nected by some means with the part of the machine which supplies the power. Suppose now the velocity from any cause to undergo a sudden increase ; by reason of the increased centrifugal force arising from the whirling motion, the balls B B will recede from the shaft D D, and raise the extremity K of the lever. On the other hand, if the velocity is diminished, the centrifugal force of the balls will be diminished, and they will fall by their own weight nearer the axes, and cause the end K of the lever to descend. When the governor is applied to a gine, the rod K I communicates with a flat circular valve V, placed in the pal steam-pipe, and so arranged that when K is elevated as fhr as the divergence of the balls will allow, the opening of the pipe will be closed by the valve V, and the passage of steam entirely stopped. On the other hand, when the balls side to their lowest position, the valve will be entirely open. Thus, when the Velocity is increased, the supply of steam is checked ; and when it is diminished, the supply of steam is immediately in creased; by which means a uniform proper velocity of the machinery is maintained.
When the governor is applied to a water wheel, the lever is made to act on the shuttle through which the water flows, and thereby controls its quantity. When applied to a windmill, it regulates the sailcloth so as to diminish the efficacy of the power upon the arms as the force of the wind increases, or vice versa.