M. B. W.--No. 1 is a silicious clay--it might be useful in the manufacture of some grades of pottery, etc. No. 2 is a ferruginous shale--contains about 80 per cent. of silica and 10 per cent. of alumina, besides lime, magnesia, iron oxide, and water.--W. S.--It is fibrous talc--talc of good quality is in considerable demand for paper making and other purposes.--W. G. H.--The sand contains no precious metal--the glittering particles are mica.--S. F.--The specimen you send consists of a mass of the long hairs which have been attached to the seeds of the "milkweed" (_asclepias_), or, as it is sometimes called, from the silky nature of these appendages, "silkweed." We believe that this material is put to no other economic use at present than that of a filling for cushions and pillows. The beauty of this silk like down long ago attracted attention, and many unsuccessful attempts have been made to put it to some practical use in the arts; but, as you have probably noticed, the hairs are both brittle and weak, and an examination with a lens will show that it wants the roughness and angularity necessary to fit it for being spun like other fibers. It has, however, been mixed with cotton and woven into fabrics having a silky luster and capable of taking brilliant dyes, but the manufacture has never been prosecuted. The plants, though widely distributed over the United States, and quite common, are nevertheless not abundant enough in a wild state to afford much of a supply, and we believe no experiments have been made in cultivating them. * * * * * Any numbers of the SCIENTIFIC AMERICAN SUPPLEMENT referred to in these columns may be had at this office. Price 10 cents each. * * * * * COMMUNICATIONS RECEIVED. The Editor of the SCIENTIFIC AMERICAN acknowledges with much pleasure the receipt of original papers and contributions on the following subjects: Manufacture of Porous Cups for Tyndall Grove Battery. By W. H. S. Cylinder Condensation. By F. F. H. Sawdust. By W. H. M. Keely Motor. By G. R. S. Firing. By A. P. A. Steam Launches. By G. F. S. * * * * * HINTS TO CORRESPONDENTS. We renew our request that correspondents, in referring to former answers or articles, will be kind enough to name the date of the paper and the page, or the number of the question. Many of our correspondents make inquiries which cannot properly be answered in these columns. Such inquiries, if signed by initials only, are liable to be cast into the waste basket. Persons desiring special information which is purely of a personal character, and not of general interest, should remit from $1 to $5, according to the subject, as we cannot be expected to spend time and labor to obtain such information without remuneration. * * * * *