How many Liquidat (c) have a purpose of dual (machine & hand composition)?
CREATE TABLE "type_metal_alloys_mentioned_in_the_uk_mo" (
  "sn_sb_pct" text,
  "liquidat_c" real,
  "solidat_c" real,
  "hardness_brinell" real,
  "purpose" text
);
SELECT COUNT("liquidat_c") FROM "type_metal_alloys_mentioned_in_the_uk_mo" WHERE "purpose"='dual (machine & hand composition)';