CHEMICAL SCIENCE. 199 



FORM OF A DROP. 



Without examination, of a. close and careful character, we are apt 

 to assume that a drop of any known fluid has one form. It is round : 

 and whether it be a drop of oil, a drop of water, a drop of ether, or 

 any other of the innumerable fluids which are known, they all appear 

 to be round. Prof. Tomlinson, of King's College, London, finds, how- 

 ever, if we examine drops of different liquids under certain conditions, 

 that each drop assumes a form peculiar to its own kind of liquid, by 

 which it may be known and identified. A drop of otto of lavender 

 puts on one shape, a drop of turpentine another. Drops of sperm-oil, 

 olive-oil, colza-oil, naptha, creosote indeed, each individual drop, be 

 the fluid what it may can be easily recognized by its form. In order 

 to test any of these forms or shapes, we have but to place a drop of 

 the fluid under examination upon water. For this purpose, we must 

 employ a glass to hold the water, taking the greatest care that it is 

 quite clean ; it must even be rinsed after being wiped, lest there be the 

 least dust from the cloth adhering to the vessel. The glass being then 

 filled with distilled or clean filtered river water, we let fall upon it a 

 drop of the fluid, and watch the shape or form it puts on. A very lit- 

 tle practice will show how easy it is thus to distinguish a drop of one 

 fluid from that of another. Even more ; if one fluid be mixed with an- 

 other, for any sinister motive or design, we can thus detect the mix- 

 ture, because we can see each fluid in one drop of the mixture. Thus, 

 by the examination of one drop of sperm-oil adulterated with one- 

 twentieth of colza-oil, the mixture is instantly discovered. So, if tur- 

 pentine be mixed with otto of lemons, or otto of lavender, we have now 

 a ready mode of discovering the cheat. Scientific American. 



SUBSTITUTION OF SOLUBLE GLASS FOR THE RESINOUS SOAP 

 USED IN THE MANUFACTURE OF ORDINARY SOAP. 



In many countries, but especially America, enormous quantities of 

 colophony have long been used in making hard brown or yellow soap. 

 These compound soaps are very useful, and in point of cheapness no 

 other soap can compete with resinous soap. The civil war in America, 

 by causing the blockade of the ports of the Slave States, whence most of 

 the resin is derived, has induced an extraordinary rise in the price of 

 colophony, so that the further manufacture of cheap soaps seemed for 

 the time arrested. 



To meet this difficulty, the attention of soap-makers has been di- 

 rected to the preparation of soaps containing silicate of soda, or the 

 so-called " soluble glass." This idea is by no means new, and has been 

 for some time practically introduced in England ; but the process 

 lately introduced into the United States differs notably from those 

 previously in use, by making use of a product rich in silica, capable of 

 forming a hard and comparatively neutral soap, instead of extremely 

 alkaline mixtures, as in England. 



The American process commences in preparing, by the dry way, a 

 silicate of soda containing five equivalents of silica and two of soda, 

 which is dissolved by prolonged boiling in water. The solution is 

 sometimes hastened by pressure. The limpid solution, freed from all in- 

 soluble impurities, is decanted and concentrated to about 35 B. ; 



