ON THE PROGRESS OF SCIENCE. IX 



he and I formerly announced, of a land shell, or pupa, in the coal 

 formation of Nova Scotia. When we contemplate the vast series of 

 formations intervening between the tertiary and carboniferous strata, 

 all destitute of air-breathing Mollusca, at least of the terrestrial class, 

 such a discovery affords an important illustration of the extreme 

 defectiveness of our geological records. It has always appeared to 

 me that the advocates of progressive development have too much 

 overlooked the imperfection of these records, and that, consequently, 

 a large part of the generalizations in which they have indulged in 

 regard to the first appearance of the different classes of animals, 

 especially of air-breathers, will have to be modified or abandoned. 

 Nevertheless, that the doctrine of progressive development may con- 

 tain in it the germs of a true theory, I am far from denying." 



One of the most interesting of recent contributions to Chemical 

 Science, is a Memoir by the well-known Swiss Chemist, Schonbein, 

 " On the result of twenty years study .of oxygen." The principal 

 points which he desires to establish are as follows : He recognizes the 

 existence of oxygen in three conditions. One, ordinary oxygen, that 

 which we respire from the atmosphere ; the two other kinds are two 

 forms of ozone, which bear the same relation to each other that the 

 two forms of electricity possess. In fact, says Schonbein, we form 

 ordinary oxygen when we bring these two kinds of ozone together ; 

 and, on the other hand, ordinary oxygen is destroyed when, by any 

 given chemical action, one of these two allotropic modifications that 

 compose it is removed. 



The tendency, on the part of the two modifications, to be produced 

 from ordinary oxygen, explains certain effects heretofore called 

 catalytic, which have been unaccountable. Thus, peroxide of barium 

 and oxygenated water, being acidified by nitric acid, are reciprocally 

 decomposed, giving rise to the formation of water, protoxide, of 

 barium, and ordinary oxygen; under similar circumstances, permanga- 

 nate of potassa is reduced to manganic oxide, and chromic acid be- 

 comes oxide of chrome ; that is to say, these compounds are deoxi- 

 dized in the presence of an abundant source of oxygen, and precisely 

 from the contact of that particular form of oxygen, or ozone, whose 

 oxidizing properties are effective in the direct oxidation of the least 

 oxidizable bodies, such as nitrogen, which is, as we know, directly 

 transformed, under the influence of ozone, into nitric acid. These 

 effects, so contradictory, are thus explained by Schonbein : A com- 

 bination strongly oxygenous can be decomposed in the presence of 

 a compound, rich in oxygen, whenever one of the compounds contains 

 oxygen in the condition that may be called positive, and the other 

 in that which may be called negative. The result of this decomposi- 

 tion is ordinary, or neutral oxygen. It is thi?, .moreover, which is 

 obtained, Avhen we experiment with ozone obtained with phosphorus 

 by the action of oxygenized water the product being pure water and 



