628 



PRESS, HYDRAULIC 



of one inch and a half by evaporation, and it is now but 1 foot 9 inches. Again in 

 the ' firing ' of the bisque-oven, its most severe ordeal, it is diminished 3 inches, and 

 is then but 18 inches high, being 6 inches or one-fourth less than the original. Now, 

 as the contraction should equally affect every portion of the details of the work, in 

 order to realise a faithful copy, and as added to this contingency are the risks in the 

 oven of being ' over-fired ' by which it would be melted into a mass, and of being 

 ' short-fired,' by which its surface would be imperfect, it is readily evident that 

 a series of difficulties present themselves which require considerable practical 

 experience successfully to meet. Indeed, the difficulties which surround the manu- 

 facture of Parian prevent its being rendered to the public at such a price as those 

 would desire who wish to secure the introduction, amongst the people, of all 

 examples which are calculated to refine their tastes. A biscuit-china is, by a some- 

 what similar process, employed in several of the porcelain-manufactories on the Con- 

 tinent for the production of statuettes, busks, &c., but in coloxir and character they are 

 all inferior to the English Parian. See BRICKS ; CLAY ; TILES. 



Our Exhortations of earthenware and chinaware have been as follow : 



1866 

 1,685,864 



1867 

 1,666,054 



1868 



1,682,721 



1869 



1,827,798 



1870 

 1,746,153 



1871 

 1,731,483 



1872 

 1,936,187 



1873 

 2,048,872 



POUDRE BARYTIQTTE. See EXPLOSIVE AGENTS. 



POWDER, COX.OXXA. See EXPLOSIVE AGENTS. 



PRECIPITATE is any matter separated in minute particles from a fluid holding 

 matter in solution, which subsides to the bottom of the vessel in a pulverulent form. 



PRECIPITATE, RED. Red oxide of mercury. 



PRECIPITATE, "WHITE. An ammoniacal chloride of mercury. 



PRESS, HVDRAtTXiIC. Though the explanation of the principles of this power- 

 ful machine belongs to a work upon mechanical engineering rather than to one upon 

 manufactures, yet as it is often referred to in this work, a brief description of it can- 

 not be unacceptable to many of our readers. 





1663 



1664 



The framing consists of two stout cast-iron plates, a, b, which are strengthened by 

 projecting ribs, not seen in the section,^. 1663. The top or crown-plate b, and the 

 base-plate a, a, are bound most firmly together by 4 cylinders of the best wrought 

 iron, c, c, which pass up through holes near the ends of the said plates, and are fast 

 wedged in them. The flat pieces e, e, are screwed to the ends of the crown and base- 

 plates, so as to bind the columns laterally. /, is the hollow cylinder of the press, 

 which, as well as the ram g, is made of cast iron. The upper part of the cavity of 

 the cylinder is cast narrow, but is truly and smoothly rounded at the boring-mill, so 

 as to fit pretty closely round a well-turned ram or piston ; the under part of it is left 

 somewhat wider in the casting. A stout cup of leather, perforated in the middle, is 

 put upon the ram, end serves as a valve to render the neck of the cylinder perfectly 

 water-tight by filling up the space between it and the ram ; and since the mouth of 



