In a 500-ml. three-necked flask, equipped with a stirrer, a reflux condenser, and a dropping funnel, is placed 140 ml. (34 g.; 2 moles of ammonia) of concentrated ammonium hydroxide solution, and 95 g. (1.3 moles) of methyl isothiocyanate (p. 599), b.p. 115–121°, is added, with stirring, over a period of 1 hour (Note 1). After the addition has been completed, the condenser is removed and the solution is heated on a water bath for 30 minutes to remove excess ammonia. The solution is then boiled with 2 g. of Norit and filtered, and the filtrate is chilled in an ice bath. The methylthiourea crystallizes as a colorless, compact, solid mass, which is collected on a filter, washed three times with 25-ml. portions of ice water, and dried. The first crop of crystals weighs 65–75 g. A second crop amounting to 15–20 g. is obtained by concentrating the mother liquor and washings to a volume of 75 ml. and again chilling in the ice bath. The total yield of methylthiourea, m.p. 119–120.5° (Note 2), is 85–95 g. (74–81%) (Note 3) and (Note 4).