and Laboratory Methods. 1651 



Make a mixture AgNOg and PbNOg, acidify with HNO3, then add a drop or 

 two of dilute H2SO4 and finally a fragment of (NH4)2 Cr207. 



Repeat the last experiment, adding this time the (NH4)2 Cr^0.j first, and 

 then the H2SO4. 



Test several different preparations containing mixtures of the calcium group 

 and silver. 



Test a mixture of AgNOg and HgNOg. 



Make a rather concentrated neutral test drop of AgNOg, add a tiny crystal 

 of Na2S04. Study the Ag2S04, which soon separates. Then add to the 

 preparation a fragment of (NH4)2 Cr207. Note well all that takes place. If 

 a selenate is at hand, substitute it in a new preparation for the Nag SO 4. 

 Cornell University. E. M. ChamOT. 



A Finish for Laboratory Table-tops. 



The following simple method for finishing the tops of laboratory tables gives 

 them a good appearance and furnishes a surface not easily acted upon by alcohol 

 and the other more usual reagents. It consists of three procedures : 



I. By means of a woolen cloth apply to the freshly planed and sandpapered 

 surface of the table a mixture consisting of equal parts of turpentine and linseed 

 oil, using it freely, and rubbing it in evenly and well. Let it dry two or three 

 days. 



II. Dissolve in turpentine shavings of yellow beeswax until the mixture forms 

 a jelly which, at ordinary temperature, is of about the consistency of vaseline, 

 becoming a clear liquid when slightly warmed. 



Apply this warm by means of a woolen cloth, rubbing it in as in the case of 

 the first mixture, and let it dry over night. 



III. Polish by rubbing, first, with a brick or a flat-iron covered with woolen 

 cloth, and then with a piece of dry cloth held in the hand. The heavy object 

 removes the superfluous wax, but leaves the surface dull, while repeated slight 

 rubbing of the second cloth produces a slight polish or gloss. 



I have not as yet observed the results of this method long enough to test its 

 lasting power, or how far it will resist the various reagents, but think it probable 

 that an occasional re-application of the wax and turpentine would be advisable, 

 to keep the surface in good condition. Regarding resistance to reagents, the 

 method is seen to consist essentially of filling the surface pores of the wood with 

 wax, which naturally repels all aqueous solutions and which would be but slightly 

 affected by alcohol. Turpentine or xylol will, of course, dissolve the wax, but 

 an injury so caused is hardly noticeable and may be easily repaired by a local 

 application of the wax solution. Inks and staining fluids seem in general to be 

 repelled by the wax, at least for a short time, and, if wiped away within a few- 

 minutes, leave no mark. 



In general appearance a table-top finished in this way compares favorably 

 with other methods of finishing woodwork, and does not give the unfinished 

 appearance of table-tops left in the natural state. 



Smith College. HARRIS HaWTHORNE WILDER. 



