560 REPORT — 1880. 



distributable. An experiment made to test this conclusion showed tliat the contact 

 of arable earth with the solution of sulphate of lime is attended by an actual sub- 

 stitution of magnesia for lime. If this notion be correct, it points to a cheaper 

 mode of supplying magnesia to the soil than to add sulphate of magnesia to manures, 

 for it follows ithat the use of gypsum in conjmiction with comparatively small doses 

 of magnesian lime will effect all that is necessary in cases in which heavy carriage 

 interferes with the use of an abundant supply of that substance. 



In conclusion, though any one of the above proofs of the value and importance 

 of magnesia in a manure may not carry conviction with it, yet taken altogether the 

 evidences are overwhelming against the notion that soil naturally contains so much 

 magnesia that an extra supply will be of little or no benefit. Moreover, there are 

 strong grounds for supposing, as we have already indicated, that magnesia, like 

 phosphoric acid, is not only an essential ingredient of plants, and aids in their 

 nutriment, but that it determines also the beneficial action of the other ingredients. 



7. On the Action of Oils on Metals. By William H. Watson, F.G.8. 



Beferring to a previous paper read by him at the last Plymouth meeting, on 

 the action of oils on copper, the author now makes the comparison between the 

 action of various oils on copper and on iron, and shows that they act very diffe- 

 rently on the two metals. He finds in several instances that those oils which act 

 little on copper act proportionately greatly on iron, while those which act little on 

 iron act greatly on copper. Thus linseed and olive oils, which act the most on 

 copper, act much less than either sperm or colza on iron. Almond oil also acted 

 very slightly on iron (in fact, with the exception of paraffin and the special lubri- 

 cating oil, it had the least action of any of the oils examined), but on copper the 

 action was great. 



Five hundred-grain measures of each oil were poured over a piece of bright 

 sheet iron, exposing 8 square inches of surface. After being kept thus exposed in 

 beakers during twenty-four days, the appearances weie noted and determinations 

 made of the iron in the oils, with the following results : — 



F.I.G., F.G.S. Berlin. 

 Preliminary iNVEsiiGA-noN. 



W. Hodges, 



Persoz,^ in describing the preparation of a solution of chloride of lime for 

 bleaching purposes, has laid great stress on the necessity for allowing the solution 

 to rest, so that the insoluble matters may subside ; as, he says, without this precau- 

 tion great risk is run in employing a solution which is not perfectly clear and trans- 

 parent, as he has perceived that the small insoluble particles held in suspension are 

 liable to find their way into the interstices of the fabrics being bleached, and on 

 these being afterwards passed through the acid bath these particles are decom- 

 posed, and chlorous and hypochlorous acids are liberated, which burn the goods, 

 producing holes in numerous places. This, he says, is of frequent occurrence in 



' Traite theorique et pratique de V Impression des Titsves. 



