referring to fig1 a device for killing moss comprises a trough 10 which is preferably mounted horizontally along the ridge 11 of roof 12 for pooling rainwater to treat a roof panel 14 covered by patches of moss 15 . the trough ordinarily extends along the entire length of the roof panel , but can be made in any length desired . referring to fig2 the trough has side walls 16 and 18 connected by a bottom wall 20 to define a generally u - shaped cross - section having an upwardly facing opening 22 for catching and pooling rainwater . each end of the trough is closed by an end wall 24 ( fig1 ). drainage means for gradually draining the rainwater onto the roof can be as simple as allowing the trough to overflow when it is full . other forms of drainage means are described hereinafter . the trough can be attached to the roof by nails 26 pounded through side wall 16 near the ridge of the roof at suitable intervals along its length . since the trough can be relatively small , for example less than one inch ( 2 . 5 cm .) across opening 22 , nails 26 are usually sufficient to support the trough even when filled with water 27 . when a larger trough size is required for a large roof panel , braces 28 ( fig7 ) can be added on the lower side of the trough . the device also includes quantities of at least two elemental metals . such metals should be capable of reacting galvanically in the presence of water to produce water soluble ions . the ion of at least one such metal must have biocidal characteristics that are effective on moss . lead and copper together provide these characteristics , although other combinations of metals , such as zinc and iron , may work as well . one or more such metals can be incorporated into the body of the trough or can be dispersed on the trough , which can be made , for example , of plastic . several configurations of such troughs are described in the following alternative embodiments . in the trough of fig2 the walls of the trough are made of ion - producing metals . such a trough can be constructed of an elongated , multi - layered , bimetallic strip 30 ( fig3 ) which has been partially folded or cupped along its length to achieve the u - shaped cross - section of fig2 . the strip is formed of at least two layers 32 , 34 of different metals , such as copper and lead . small holes 36 are punched through the strip before folding it to expose the junctions of the layers to the captured rainwater and to slowly drain the water onto the rooftop . lead sheets of 16 - gauge thickness and copper sheets of 14 - gauge thickness provide layers of suitable thickness , although these dimensions can be varied . referring to fig4 the layers need not be bonded together because nails 26 and punched holes 36 provide sufficient contact between the layers for electrolysis to occur around the holes . in addition , any gaps 38 between the layers will admit water and air into regions of contact between the holes where electrolysis can also occur . holes 36 are preferably positioned in a row extending along side wall 18 . multiple rows of holes can also be used , as shown in fig6 . the holes are punched with a one - penny nail or a similarly sized punch . this operation produces holes having a diameter of about 1 / 32 &# 34 ; ( 0 . 8 mm ). punching the holes from the inner surface 42 of the trough squeezes the layers of metal together around each hole to form regions of contact between adjacent faces of the layers . it also produces a droplet - forming nipple 44 on the outer surface 46 of the trough . thus , a cylindrical surface 48 defines an exposed bimetallic junction 50 at which electrolytic action can occur when water 27 is present . the small diameter of the holes , aided by surface tension of the water as it forms droplets 52 in the nipples , controls the rate of leakage of water from the trough so that water remains in prolonged contact with the bimetallic junction and can thus dissolve more of the metal than otherwise . such construction results in stronger biocidal solutions than were available from previous metal strip designs . in trough 10a of fig5 an inner layer 52 of copper is sandwiched between two outer layers 54 , 56 of lead to form triple - layered trough walls . the lead layers can be separate sheets or , as shown in trough 10b of fig6 can be a single sheet folded around one edge of the copper sheet . in all other respects the troughs of fig5 and 6 resemble that of fig2 . the three - layer construction is somewhat preferred over the two layer design in that it provides two lead - copper junctions 60 , 62 at which galvanic action can occur in the presence of water , but it is more costly to construct . in fig7 the trough 10c itself can be either metallic or nonmetallic . for example , the trough can be made of split plastic pipe , and the ion - producing metals are chips or pieces 64 of lead and copper deposited in the trough , preferably with the bimetallic pieces in contact with one another . alternatively , the trough can be made of split pipe of one metal , such as copper , having pieces of a second metal , such as lead , dispersed therein . this design is particularly useful on large roof - tops which require a larger trough to capture and release a greater quantity of moss - killing solution than is required by small rooftops . using split pipe rather than a multi - layered metal trough reduces the cost of materials for large troughs . it also permits replenishment of the ion - producing metals without replacing the entire trough . ordinarily , braces 28 are used to mount trough 10c . however , small split - pipe troughs can be mounted using nails . holes 36c are preferably drilled in plastic pipe troughs because the elasticity of the plastic makes punching such holes difficult . alternatively , vertical slots can be cut in wall 18c as shown in fig1 to provide a controlled drainage means . trough 10d in fig8 is similar to trough 10 of fig2 except that wall 16d of fig8 is straight rather than curved so that it can fit beneath the lower edge of ridge shingle 66 . trough 10e in fig9 is similar to trough 10d of fig8 except that layers 32e and 34e in fig8 only contact each other in the region 68 of wall 16e . layer 32e is curved upwardly about an axis of curvature which is closer to ridge 11 than the axis of upward curvature of layer 34e . thus , trough 10e provides two upwardly - open trough portions 70 , 72 rather than the single trough of the fig2 embodiment . rainwater is collected in a lower pool 27a by trough portion 70 and in an upper pool 27b by trough portion 72 . the water in pool 27a contacts both layers 32e and 34e in region 68 to facilitate electrolysis of the two metals . such water gradually leaks through holes 36e onto the rooftop , carrying ions of the two metals with it . water in pool 27b gradually drains through holes 36f into pool 27e . by making holes 36f smaller than holes 36e , pool 27b drains more slowly than pool 27a . thus , the upper pool replenishes the lower pool and extends the time over which water in the lower pool dissolves the metal and drains onto the rooftop . in fig1 vertical notches 74 replace holes 36e , 36f of the trough of fig9 . in fig1 , a scalloped upper edge 76 of layer 32e replaces holes 36f of fig6 . each undulation in layer 32e forms a lip 78 which allows water to pour into the pool below . numerous other drainage means for controllably releasing water onto the roof can also be used . examples not shown in the drawings include long narrow slots in a side or bottom wall of the trough , overflow lips similar to lips 78 , and a pervious side or bottom wall . fig1 and 11 also depict a unitary end wall 80 which can substitute for end wall 24 . such a wall is formed by cutting layers 32 , 34 along dashed lines 82 , 84 in fig3 removing portion 86 , and folding portions 88 , 90 upwardly until they meet at corner 92 . some leakage at corner 92 is permissible . having illustrated and described several preferred embodiments of the invention , it should be apparent to those skilled in the art that the invention may be modified in arrangement and detail . i claim as my invention all such modifications as come within the true spirit and scope of the following claims .
a device for killing moss on rooftops comprises an elongated bimetallic trough for horizontal positioning along a rooftop to catch rainwater . in one embodiment the walls of the trough include a layer of copper and a layer of lead sandwiched together . small holes through such layers , and spaced apart in rows along a wall of the trough , slowly drain the rainwater onto the rooftop . as the water passes through the holes , contacting the junction of the lead and copper layers , an electrolytic action occurs in which ions of the metal dissolve into the water . the resultant electrolyte kills the moss . another embodiment comprises a plastic trough having holes in one side and containing pieces of lead and copper .