TRANSACTIONS OP THE SECTIONS. 75 



improved the discovery. The means which lie employs to effect the preservation of 

 milk is still heat; hut heat applied in some peculiar way, by manual dexterity, first 

 discovered by a Swiss shepherd. All that I am allowed to state is that the effect of 

 this new method of applying heat is to remove a sort of diustore, or animal ferment, 

 which exists in milk in a very small quantity, and which is the real cause of its 

 speedy decomposition. When this species of ferment is removed, milk can be pre- 

 served for an indefinite period of time in vessels not quite full, and consequently 

 exposed to the contact of rarefied air, a result which was not effected by the process 

 of M. Maben, or rather that of M . Gay-Lussac, as they completely expelled those 

 gases which otherwise would have rendered it sour. I have such full confidence in 

 the success of M. de Pierre's process, that I had not the least hesitation in bringing 

 along with me from Paris to Aberdeen a large vessel containing five gallons of milk, 

 fearlessly trusting it to railroads and steam-boats, thus exposing it to all the incidents 

 of the journey. I am so confident of the success of the process, that I pour out the 

 contents of this large vessel into Scotch glasses with the conviction that I am giving 

 to the ladies and gentlemen of the British Association a milk as natural, as pure, and 

 as rich as when it was taken from the cow in the fertile plains of Normandy. May 

 this potion, so sweet and so pure, be a symbol of those sentiments of benevolent 

 affection, which France, flourishing and enlightened, entertains towards her noble and 

 great sister England ! Owing to its greater specific lightness cream ascends to the 

 top of the vessel, but it can be easily made to diffuse itself through the milk by slightly 

 shaking it before uncorking the bottle. As the vessel is not quite full, a small 

 quantity of butter may have been formed, and the milk may have become somewhat 

 less rich, but it will still be pure and natural milk without any strange taste. Thanks 

 to the progress of science, of which I am happy to be the representative, France can 

 yield with profit to England her fruits, her vegetables, her eggs, and now offers her 

 prepared milk for the wants of the army and navy, having nothing to fear from the 

 longest voyages, nor from the excesses of heat and cold. 



Quantitative Estimation of Tannin in some Tanning Materials. 

 By Messrs. Mulligan and Dowling. 



On Marsh's Test for Arsenic. By W. Odling, M.B., F.R.S., F.C.S. 



Marsh's test depends upon the production of arseniuretted hydrogen when 

 arsenical substances are in presence of nascent hydrogen. The author showed that 

 numerous and varied bodies, including animal tissue, vegetable tissue, the organic 

 matter contained in ordinary earth, preparations of copper and mercury, and oxidi- 

 zing salts, prevented the formation of arseniuretted hydrogen, and thereby defeated the 

 action of Marsh's test. As a mode of separating the arsenic from these interfering 

 substances, the author recommended the process of distillation with muriatic acid, 

 whereby arsenic in the form of terchloride of arsenic is isolated in a form suitable 

 for testing by Marsh's process. 



On the Composition of Thames Water. 

 By W. Odling, M.B., F.R.S., and A. Dupre, Ph.D., F.C.S. 



The general conclusions were as follows : — The amount of dissolved matter, organic 

 and mineral, is greater in high than in low water, in consequence of the contamination 

 of the high water with sea-water — greater in summer than in winter, in consequence 

 of the greater contamination with sea-water in that season, dependent upon the dimi- 

 nished volume of the fresh stream-water. In the winter and early spring, when the 

 quantity of stream-water is great, the presence of sea- water scarcely makes itself felt 

 in the high water, even at Greenwich ; or, in other words, there is very little difference 

 in the saline matter of low and high water ; but in dry weather this difference becomes 

 more and more marked, and is noticeable higher and higher up the river. Early in 

 the present year, the existence of sea-water in the river was very perceptible, so much 

 so, that even at Wandsworth a difference between high and low water was observed, 

 comparable to that which existed at Greenwich during the winter months. During 

 corresponding periods, the average amounts of residue in high and low water at 



