VOL. LXXVII.J PHILOSOPHICAL TRANSACTIONS. 271 



among the Europeans who have settled there, the dogs are more of a mixed breed; 

 for why they should only have had this kind of dog transported among them, 

 while every other part of America has the varieties of Europe, is not easily 

 solved. 



The voice of animals is commonly characteristic of the species ; but I should 

 suppose it is only characteristic of the original species, and not always of the 

 variety, and this supposition holds good in the dog species. It would appear, 

 that the voice-of the wolf and the jackal is very similar, and is principally con- 

 veyed through the nose, and exactly resembles that noise in dogs, which is a 

 mark of longing or melancholy, and also of fondness ; but has no resemblance to 

 the bark of the dog, which they do not perform. Barking is peculiar to certain 

 varieties of the dog kind, and even some that do bark, do it less than others. The 

 dogs in the South-Sea islands do not bark: our greyhound barks but little; while 

 the mastiffj and many of the smaller tribe, as spaniels, are particularly noisy in 

 this way. It would appear as if the frequency of this noise arose from imitation ; 

 for the dogs in the South-Seas learn to bark ; and others, as the hound, have a 

 peculiar howl, which by huntsmen is called the tongue. This noise, as also the 

 bark, is made by opening the mouth. A variety in the voice, or some parts of 

 the voice, in the varieties of the same species, is not peculiar to the dog. 



XXV. Experiments on the Congelation of the Vitriolic Acid. By James Keir, 



Esq.,F.R.S. p. 267. 



That the vitriolic acid sometimes assumes a solid, crystalline state, has been 

 observed by Basil Valentine, and by many later chemists ; but their relations of 

 this appearance are neither sufficiently explicit, with regard to the essential and 

 concomitant circumstances, nor do they seem very consistent with each other. It 

 appears however, that two very distinct species of congelation of this acid have 

 been noticed. That which is described by the older chemists, and also by some 

 modern authors, requires no greater degree of cold than the common temperature 

 of the air, even in summer, and is peculiar to that acid which is obtained by 

 distillation from martial vitriol, and which is possessed of a smoking quality in a 

 high degree : for not only the authors, by whom this congelation has been ob- 

 served, havc'given this description of the acid employed, but also the late experi- 

 ments of M. Dollfuss (Crell Annalen 1785) seem to show, that the smoking 

 quality is essential to the phenomenon ; for neither the acid obtained from vitriol, 

 when deprived by rectification of its smoking quality, nor the English oil of 

 vitriol (which is known to be obtained by burning sulphur, and which does not 

 smoke), were found, by his trials, to be susceptible of this species of congelation. 

 The acid thus congealed has been called glacial, or icy oil of vitriol. The other 

 kind of congelation has been little noticed till l^ely. To this congelation every 



