other solid dosage form such as a tablet. Softgels are also highly suited to potent drugs (for example, where the dose is <100 µg), where the highly reproducible filling process helps ensure each softgel has the same drug content, and because the operators are not exposed to any drug dust during the manufacturing process. In 1949, the Lederle Laboratories division of the American Cyanamid Company developed the "Accogel" process, allowing powders to be accurately filled into soft gelatin capsules. Two-piece gel encapsulation ("hard capsules") James Murdoch of London patented the two-piece telescoping gelatin capsule in 1847. The capsules are made in two parts by dipping metal pins in the gelling agent solution. The capsules are supplied as closed units to the pharmaceutical manufacturer. Before use, the two halves are separated, and the capsule is filled with powder or more normally pellets made by the process of extrusion and spheronization (either by placing a compressed slug of powder into one half of the capsule or by filling one half of the capsule with loose powder) and the other half of the capsule is pressed on. With the compressed slug method, weight varies less between capsules. However, the machinery required to manufacture them is more complex. The powder or spheroids inside the capsule contains the active ingredients and any excipients, such as binders, disintegrants, fillers, glidant, and preservatives. Manufacturing materials Gelatin capsules, informally called gel caps or gelcaps, are composed of gelatin manufactured from the collagen of animal skin or bone. Vegetable capsules, introduced in 1989, are made from cellulose, a structural component in plants. The main ingredient of vegetarian capsules is hydroxypropyl methyl cellulose. In the 21st century, gelatin capsules are more broadly used than vegetarian capsules because the cost of production is lower. Manufacturing equipment The process of encapsulation of hard gelatin capsules can be done on manual, semi-automatic, and automatic capsule filling machines. Hard gelatin capsules are manufactured by the dipping method which is dipping, rotation, drying, stripping, trimming, and joining. Softgels are filled at the same time as they are produced and sealed on the rotary die of a fully automatic machine. Capsule fill weight is a critical attribute in encapsulation and various real-time fill weight monitoring techniques such as near-infrared spectroscopy (NIR) and vibrational spectroscopy are used, as well as in-line weight checks, to ensure product quality. Volume is measured to the fill line, which is customary