216 REPORT— 1886. 



tions. We prepare the mixture by thoroughly mixing the recrystallised 

 salts, maintaining the product in a state of fusion for some little while in 

 an open dish, and subsequently powdering the solid produced on cooling. 

 The melting-point of the product is considerably lower than that of 

 either chlorate of potassium or chlorate of sodium ; and it gives off its 

 oxygen to about the same extent as chlorate of potassium ; that is to say, 

 about one-third of it is easily expelled by a moderate heat. 



In conclusion, we are glad to be able to report that we have also con- 

 structed most of the rest of the apparatus that will be required in the 

 investigation that is before us. We hope, therefore, to make considerable 

 progress before the next meeting of the Association. 



Note. — October 10, 1886. Since this report was read we have suc- 

 ceeded in connecting all the parts of the oxygen generator and holder 

 before the blowpipe by a method described by one of us.' The only 

 permanent mercury joint which remains is that at F, which is now 

 specially protected against entrance of air. We may, therefore, expect 

 to approach still nearer to the attainment of absolutely pure gases for our 

 experiments. 



Report of the Committee, consisting of Professors Tilden and 

 Armstrong (Secretary), appointed for the purpose of investi- 

 gating Isomeric Naphthalene Derivatives. 



The study of isomeric naphthalene derivatives acquires importance from 

 a variety of considerations, notably, from the very close relationship of 

 naphthalene to benzene, which finds expression in the use of a simple 

 hexagon to represent the latter hydrocarbon, the first mentioned being 

 symbolised by a double hexagon formed of two benzene hexagons joined 

 so that one side is common to both. 



In the case of benzene there are but three possible isomeric di-deriva- 

 tives, according to the received theory of the constitution of this hydro- 

 carbon ; the formation of these di-derivatives is governed by certain 

 very simple ' laws,' the first of which may conveniently be termed the 

 ^ara-law, the second the meta-\a,w : i.e., mono-derivatives containing a 

 hydrocarbon radicle, one of the halogens, NH2, or OH invariably yield as 

 chief product a para-di-derivative together with the isomeric ortho-di- 

 derivative, the meta-di-derivative being formed, if at all, to but a small 

 extent; whereas mono-derivatives containing NO2, SO3H, or COOH 

 yield as chief product the me<a-di-derivative, the para- and ortho-deriva- 

 tives being formed in relatively small amount. 



Instead of three, naphthalene may give rise to ten isomeric Ji- 

 derivatives ; it might therefore be expected that the laws of substitution 

 for naphthalene would be proportionally less simple than for benzene : 

 thus far, however, this has not been found to be the case, and many of 

 the di-derivatives are to be prepared only by indirect methods. The para- 

 law obtains equally in the case of naphthalene, being applicable to mono- 

 derivatives analogous to those which in the benzene series obey the para- 



• Methods of Glass-hlomiiig, pp. 62-3. 



