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sequence. It is of some practical importance to know the exact 
circumstances under which this takes place, and the following ex<- 
periments may prove useful in this respect. Sometimes, in distilling 
and subsequently evaporating sulphuric acid, I obtained a hydrate 
of sp. gr. 1*848, and at other times not exceeding 1*842. To ex- 
plain these differences I took — 
1. Monohydrated sulphuric acid, having the sp. gr. 1*848, and 
containing by alcametrical testing 81*62 per cent, of anhydrous 
acid, and buried the retort containing it in hot sand, and distilled. 
The distillate now contained only 80*12 anhydrous acid, and had a 
sp. gr. of 1*840 at 60° Fahr. It had lost in distillation about 1^ 
per cent of anhydrid. 
2. The weak acid thus got by distillation was exposed to a tem- 
perature near to, but not exceeding, 554° Fahr., for forty minutes. 
On cooling, its alcametrical strength was 81*615 of anhydrid, and 
its specific gravity 1*84798. 
3. A portion of the first acid, having the strength 81*62 of an- 
hydrid, and the specific gravity 1*848, was boiled violently for two 
hours. On testing, it was now found to contain only 80*01 of an- 
hydrid and to have a specific gravity of 1*838. 
4. The weak acid got in the last experiment was kept for one 
hour at a temperature of 550° Fahr. The concentrated acid thus 
got gave 81*62 anhydrid and a specific gravity of 1*84792. 
From these experiments, it follows, notwithstanding Marignac’s 
researches, that there is a real monohydrated sulphuric acid obtain- 
able by evaporation, and that its specific gravity is in reality as 
high as 1*848, which is the number formerly given in books ; but 
that this hydrate is decomposed between the temperature of 550° 
Fahr. and the boiling point of oil of vitriol. 
2. Note respecting Ampere’s Experiment for showing the 
Repulsion of a Rectilinear Electrical Current on itself. By 
Principal Forbes, LL.D., &c. 
The experiment referred to was performed in 1823 by Ampere 
in the presence of Mr A. Be la Rive. It is intended to show that 
if one portion of a rectilinear conductor is made moveable, it will be 
repelled from the portions which form its continuation. The ar- 
