CHEMICAL SCIENCE. 235 



on this subject an observation made by M. F. de Rivero is extremely 

 curious. At the places above mentioned the lowest guano deposits 

 are covered with a stratum of old alluvial soil ; then conies another 

 layer of guano, and then a stratum of modern alluvial soil. To un- 

 derstand the importance of this fact, our readers must keep in mind 

 that the age of the modern alluvions does not extend beyond our 

 historical times, while old alluvions date from the period immediately 

 preceding that at which man first began to inhabit the earth; so 

 that the guanaes, or cormorants and other allied tribes of birds which 

 deposit guano, must have existed thousands of years before man, see- 

 ing that the inferior layer of guano is several yards, sometimes from 

 fifteen to twenty, in depth, and the old alluvial crust above it has a 

 thickness of three yards. 



To explain the immense accumulation of guano in these regions, 

 M. Boussingault observes that there has been a combination of a 

 variety of causes favorable both to its production and preservation. 

 Among these causes must be reckoned a dry climate, a ground pre- 

 senting a vast number of chinks, fissures, and caverns, where the 

 birds can rest, lay their eggs, and hatch them, without being disturbed 

 by the strong breezes from the south ; and then abundance of the 

 food suited to them. Nowhere is fish so abundant as on this coast, 

 where whole shoals of them are cast upon the shore even in fine 

 weather. Antonio de Ulloa states that anchovies especially are in 

 such abundance here as to defy description ; and he gives a good 

 account of the manner in which their numbers are diminished by 

 the myriads of guanaes which are seen sometimes flying in countless 

 flocks, like clouds intercepting the sun's rays, and sometimes darting 

 into the sea to catch their prey. According to M. Boussingault's 

 calculation, 100 kilogrammes of guano contain the nitrogen of 600 

 kilogrammes of sea-fish ; and as the guano deposits, before they began 

 to be worked, contained 378,000,000 of metrical quintals of guano, 

 the birds must have consumed 2,268,000,000 of quintals offish. 



GUANO AND ARTIFICIAL PEARLS. 



Artificial pearls were invented in the fifteenth century by a Paris- 

 ian artist by the name of Jaquin. These are small beads of thin 

 glass lined in the interior with Essence d' Orient and then filled with 

 wax. But what is the substance called " essence d'orient ? " This 

 pompous name was invented for the sole purpose of concealing the 

 true nature of the material from which it was prepared. But this 

 material is furnished by a small white fish, the ablette, very common 

 in the rivers of continental Europe. It accompanies* the scales of 

 this fish, and is detached when the scales are rubbed up for a consid- 

 erable time and thrown into a vase of water. To collect the essence 

 d'orient the water is poured off from the vase upon a fine hair sieve, 

 which retains the scales and allows the water and the product sought 

 to pass through it. The latter sinks to the bottom, and is obtained 

 pure by decanting the water. A little ammonia is added to prevent 

 its decomposition. 



In one small river, in the department of Meurthe, not far from 

 Nancy, they collect each year 25,000 kilogrammes of the ablette, pro- 



