On the Separation of the Oxalic from other Organic Acids. 25 



derived from some similar source, acting on substances either 

 themselves organized, or like coal of organic origin. 

 Durham, May 1838. 



VI. On the Separation of the Oxalic from other Organic Acids. 

 By James F. W. Johnston, M.A., F.R.SS., L. ^ E. 

 F.G.S., Professor of Chemistry and Mineralogy, Durham.* 



\ T the Liverpool meeting of the British Association in 

 -^ September last, I exhibited and stated the composition 

 of a beautiful salt I had formed some months before, consist- 

 ing of an atom of nitrate with an atom of oxalate of lead and 

 two atoms of water. In the Number of the Philosophical 

 Magazine for May is given an extract of a paper by M. De- 

 jardin, in which this salt is very correctly described, and cer- 

 tainly without the knowledge of my having previously made 

 it known f. As the study of this interesting compound, how- 

 ever, has suggested an easy method of separating the oxalic 

 from other organic acids, I shall briefly describe the unpub- 

 lished observations I have made upon it. 



I prepare the salt by adding nitric acid in considerable 

 quantity to a weak solution of oxalic acid, or of acetate of 

 lead, and pouring in slowly a solution of subacetate of lead, 

 or of dilute oxalic acid. Shining plates of the compound 

 speedily begin to fall. If the quantity of oxalic acid be mi- 

 nute, or if it be largely diluted, the crystals fall only after 

 some time, and in the form of six-sided tables, of which two 

 of the sides are longer than the others, possessing a silvery 

 whiteness and peai'ly lustre, and striated longitudinally so as 

 to exhibit the most beautiful prismatic colours when light is 

 reflected from them. I have also obtained it in acicular prisms 

 nearly an inch in length, which according to the measurement 

 ofProfessor Miller of Cambridge, are oblique rhombic prisms. 



Decomposed by sulphuretted hydrogen it gives a colourless 

 solution, which, when evaporated, emits fumes of nitric and 

 yields crystals of oxalic acid. 



Heated to 212° this salt does not diminish in weight; at a 

 temperature of about 500° Fahr. it loses 2 atoms (5*425 per 

 cent.) of water, and before it reaches 570° Fahr. it has given 

 off copious red fumes, lost upwards of 19 per cent., and is 



* Communicated by the Author. 



t I may take this opportunity of mentioning, that under the name of 

 lodal, M. L'Aniy has lately described a compound of which I published 

 an account in the Edinburgh Journal of Science (II. p. 415.) some years 

 ago. It is obtained by the action of nitric acid on iodine in alcohol, and 

 has not yet been analysed. 



