Answers to Queries. 93 
and putty powder, followed by soap and water, is one of the best 
mediums for brightening brass or copper. _ To frost brass-work, 
and give it an ornamental finish, boil the article in caustic potash, 
rinse in clean water, and dip in nitric acid till all oxide is removed ; 
then wash quickly, dry in warm boxwood sawdust, and lacquer 
white warm. 
Answers to Queries. 
325.—Weight of the Earth.—Such an expression, or enquiry, 
is really meaningless. What zs the weight of anything? Simply 
the pressure or force exerted by a body in the direction of the 
earth’s centre. The substance manifesting weight must therefore 
be something distinct from the earth itself. |. What really is meant 
by the question ‘“‘ What is the weight of the earth?” probably is, 
‘*What would a body, similar in all respects to the earth, weigh, if 
brought close to the earth ?” Be Sas: 
331.—Canada Balsam. —F or mounting perfectly hard objects, as 
diatomacez, foraminifera, polycistina, or spicula, ordinary balsam 
obtained by heat is best, and in the case of diatomacez the turpen- 
tine existing in the balsam should to a great extent be evapo- 
rated before the cover is put finally down, otherwise the refractive 
index will be too low to show the markings properly. Most other 
objects will not stand the heating requisite to soften viscid balsam, 
and if they would, there might frequently be danger of producing 
vapour bubbles, which take some time to disappear. For this 
reason when we are mounting sections, insect parts, botanical 
objects, and the like, the balsam should always be thinned. With 
regard to the relative merits of benzole and chloroform there is 
considerable difference of opinion, but both are much more rapid 
driers than turpentine. The latter medium is apt to turn “ fat,” 
owing to conversion of some of the volatile oil into resin. On the 
other hand, turpentine never tends to produce cloudiness in 
balsam ; while benzine often does this, and sometimes will not 
mix with it at all well. For this reason I generally use turpentine 
with balsam. It is an excellent plan to keep only a little balsam 
out ready for use, and to add a little fresh turpentine when it gets 
thick. Unless the mounter is in a hurry to get the slides finished, 
its slow-drying propensities are not very disadvantageous. As I 
have pointed out in the Lxgwirer, for October, 1887, it will be a 
great advantage to expose the object in the balsam for a day or 
two before mounting. If this be not convenient it is still expedient, 
wherever possible, to harden the balsam after mounting, by placing 
