PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 339 



calls it nitrum, and relates the circumstances attending the discovery of 

 glass by its accidental fusion with silica, on the shore where the sailors 

 were using it to support their kettles while cooking their dinner. 



The difference between soda and potassa was not known to the ancients, 

 and this was first recognized by Duhamel in 1735. The alchemists were of 

 the opinion that the alkali of plants was produced by the burning, and it 

 was not until 1764 that it was shown to be present in the living plant. 



According to Pliny, the Romans learned the art of soap making from 

 the Gauls. 



Pliny says: "Soap is an invention of the Gauls, and is used for giving 

 a I'eddish tint to the hair. It is prepared from tallow and ashes, the ashes 

 of beech and elm being preferred; there are two kinds of it, the hard and 

 the liquid, both of them much used by the people of Germany, the men in 

 particular more than the women." 



The city of Pompeii contained a complete soap-boiling establishment. 

 It was near the sea shore, conveniently placed for the importation of the 

 blocks of soda (niter) from Syria, and next door to the custom-house. The 

 works were uncovered, after having been buried more than 1,700 years, and 

 found in a tolerable state of preservation. 



The first room contained lime soap. In the second were five oval vessels 

 made of cement and coated with hard stucco, which had been used in the 

 manufacture of soap It is a curious fact that the pumice stones which 

 rained down upon Pompeii and drove out the soap boiler of that day, 

 are now ground up and used by our manufacturers in the preparation of 

 sand soaps. Whatever may have been the origin of this manufacture, it is 

 clear that it was carried on in a thoroughly empirical manner for many 

 centuries. We are indebted to a man still living for our knowledge of the 

 scientific principles which lie at the foundation of this important industry. 

 The French chemist, Chevrenl, first announced to the Academy of Sciences 

 in Paris, in a paper dated July 5, 1813, his discovery of the compound 

 nature of the fatty bodies. Previous to that time, fat had been regarded 

 as an unmixed organic substance; Chevreul showed it to be composed of 

 several salts, which he called stearine, margarine and olein. These bodies 

 will be described by the gentleman who is to follow me. 



The influence of Chevreul's discovery upon the manufacture of soap and 

 candles was immense; and so great has the industry become that all parts 

 of the world have been laid under contribution for the supply of the raw 

 material. There is an oft quoted sentence in Liebig's Letters on Chemistry: 

 " Die Seife ist ein Massetab faer den Wohlstand und die Cultur der Staafen.'' 

 (Soap is a measure of the prosperity and civilization of a people.) 



Liebig refers to the endless threads of manufacture which are bound up 

 with this industry. 



The extensiVe supply of soda ash has suggested its use in the manu- 

 facture of glass and in the preparation of soap. Sulphuric acid was neces- 

 sary in its manufacture, and the supply of this acid became so great that 

 its application increased in proportion. To make sulphuric we need nitric, 

 and for nitric we send to explore and civilize South America, and obtain 

 nitrate of soda, and thus diminish the demand for saltpeter and render 

 that available for gunpowder. Hydrochloric acid is an incidental product 



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